# EDGAR Filing Document

**Accession Number:** 0001326190
**File Stem:** 0001326190-25-000073
**Filing Date:** 2025-11
**Character Count:** 113834
**Document Hash:** 04951399e1e19ab9503484c49022b25a
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001326190-25-000073.hdr.sgml**: 20251113

**ACCESSION NUMBER**: 0001326190-25-000073

**CONFORMED SUBMISSION TYPE**: S-3/A

**PUBLIC DOCUMENT COUNT**: 3

**FILED AS OF DATE**: 20251113

**DATE AS OF CHANGE**: 20251113

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Altimmune, Inc.
- **CENTRAL INDEX KEY:** 0001326190
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 202726770
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** S-3/A
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-291329
- **FILM NUMBER:** 251479895

**BUSINESS ADDRESS:**
- **STREET 1:** 910 CLOPPER ROAD
- **STREET 2:** SUITE 201S
- **CITY:** GAITHERSBURG
- **STATE:** MD
- **ZIP:** 20878
- **BUSINESS PHONE:** 2406541450

**MAIL ADDRESS:**
- **STREET 1:** 910 CLOPPER ROAD
- **STREET 2:** SUITE 201S
- **CITY:** GAITHERSBURG
- **STATE:** MD
- **ZIP:** 20878

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** PHARMATHENE, INC
- **DATE OF NAME CHANGE:** 20071016

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** HEALTHCARE ACQUISITION CORP
- **DATE OF NAME CHANGE:** 20050505

[**Table of Contents**](#TOC)

**As filed with the Securities and Exchange Commission on November 13, 2025**

**Registration No. 333-291329&nbsp;&nbsp;&nbsp;&nbsp;**

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**UNITED STATES**

**SECURITIES AND EXCHANGE COMMISSION**

**Washington, D.C. 20549**

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**AMENDMENT NO. 1**

**TO**

**FORM S-3**

**REGISTRATION STATEMENT**

***UNDER***

***THE SECURITIES ACT OF 1933***

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**ALTIMMUNE, INC.**

**(Exact Name of Registrant as Specified in its Charter)**

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| | | |
|:---|:---|:---|
| &nbsp;&nbsp;**Delaware** | &nbsp;&nbsp;**2834** | &nbsp;&nbsp;**20-2726770** |
| &nbsp;&nbsp; **(State or Other Jurisdiction of Incorporation or Organization)** | &nbsp;&nbsp;**(Primary Standard Industrial**<br>**Classification Code Number)** | &nbsp;&nbsp;**(I.R.S. Employer**<br>**Identification No.)** |

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**910 Clopper Road, Suite 201S**

**Gaithersburg, Maryland 20878**

**Telephone: (240) 654-1450**

**(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant's Principal Executive Offices)**

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**Dr. Vipin K. Garg**

**Chief Executive Officer**

**Altimmune, Inc.**

 **910 Clopper Road, Suite 201S**

**Gaithersburg, Maryland 20878**

**Telephone: (240) 654-1450**

 **(Name, address, including zip code, and telephone number, including area code, of agent for service)**

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***Copy to:***

**Joseph C. Theis, Jr.**

**Justin S. Anslow**

**Goodwin Procter LLP**

**100 Northern Avenue**

**Boston, Massachusetts 02210**

**Telephone: (617) 570-1000**

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**Approximate date of commencement of proposed sale to the public:** From time to time or at one time as determined by the Registrant after the effective date of this registration statement.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. ☐

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box. ☒

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If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ☐

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company" and "emerging growth company" in Rule 12b-2 of the Exchange Act:

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| | | | |
|:---|:---|:---|:---|
| Large accelerated filer | ☐ | Accelerated filer | ☐ |
| Non-accelerated filer | ☒ | Smaller reporting company | ☒ |
| Emerging growth company | ☐ |  |  |

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If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐**.**

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**The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.** 

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#### EXPLANATORY NOTE
This Amendment No. 1 to the Registration Statement on Form S-3 (Registration No. 333-291329) of Altimmune, Inc. is being filed solely for the purpose of including language provided by Rule 473(a) of the Securities Act of 1933, as amended, for the delayed effectiveness of this registration statement following the filing of this Amendment No. 1.

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**The information in this preliminary prospectus is not complete and may be changed. These securities may not be issued until the registration statement filed with the U.S. Securities and Exchange Commission is effective. This preliminary prospectus is not an offer to sell these securities and does not constitute the solicitation of an offer to buy these securities in any jurisdiction where the offer or sale is not permitted.**

**SUBJECT TO COMPLETION, DATED NOVEMBER 13, 2025**

**PRELIMINARY PROSPECTUS**

**$400,000,000**

**Common Stock**

**Preferred Stock**

**Debt Securities**

**Warrants**

**Units**

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We may from time to time issue, in one or more series or classes, up to $400,000,000 in aggregate principal amount of our common stock, preferred stock, debt securities, warrants and/or units. We may offer these securities separately or together in units. We will specify in the applicable accompanying prospectus supplement the terms of the securities being offered. We may sell these securities to or through underwriters and also to other purchasers or through agents. We will set forth the names of any underwriters or agents, and any fees, conversions or discount arrangements, in the applicable accompanying prospectus supplement. We may not sell any securities under this prospectus without delivery of the applicable prospectus supplement.

You should read this document and any prospectus supplement or amendment carefully before you invest in our securities.

Our common stock is listed on The Nasdaq Global Market under the symbol "ALT." On November 5, 2025, the closing price for our common stock, as reported on The Nasdaq Global Select Market, was $3.75 per share. Our principal executive office is located at 910 Clopper Road, Suite 201S, Gaithersburg, Maryland 20878.

**Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties referenced under the heading "**[**Risk Factors**](#RISKFACTORS_Prospectus)**" contained in this prospectus beginning on page 2 and any applicable prospectus supplement, and under similar headings in the other documents that are incorporated by reference into this prospectus.**

**Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.**

**The date of this prospectus is , 2025.**

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**TABLE OF CONTENTS**

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| | |
|:---|:---|
|  | **Page** |
| [About This Prospectus](#ABOUTTHISPROSPECTUS_42553) | 1 |
| [Risk Factors](#RISKFACTORS_852925) | 2 |
| [Cautionary Statement Regarding Forward-Looking Statements](#SPECIALNOTE_891720) | 3 |
| [Our Company](#ALTIMMUNEINC_198234) | 4 |
| [Use of Proceeds](#USEOFPROCEEDS_520331) | 6 |
| [Securities We May Offer](#SecuritiesWeMayOffer) | 7 |
| [Description of Capital Stock](#DESCRIPTIONOFCAPITALSTOCK_39358) | 8 |
| [Description of Debt Securities](#DESCRIPTIONOFDEBTSECURITIES_48288) | 12 |
| [Description of Warrants](#DESCRIPTIONOFWARRANTS_481136) | 18 |
| [Description of Units](#DESCRIPTIONOFUNITS_569510) | 19 |
| [Plan of Distribution](#PLANOFDISTRIBUTION_971168) | 22 |
| [Legal Matters](#LEGALMATTERS_137637) | 25 |
| [Experts](#EXPERTS_307999) | 26 |
| [Where You Can Find More Information](#WHEREYOUCANFIND_208398) | 27 |
| [Incorporation by Reference](#INCORPORATION_872618) | 28 |

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#### ABOUT THIS PROSPECTUS
This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or the SEC, utilizing a "shelf" registration process. Under the shelf registration, we may offer shares of our common stock and preferred stock, various series of warrants to purchase common stock or preferred stock, debt securities or any combination thereof, from time to time in one or more offerings.

This prospectus provides you with a general description of the securities we may offer. Each time we sell securities, we will provide one or more prospectus supplements that will contain specific information about the terms of the offering. The applicable prospectus supplement may also add, update or change information contained in this prospectus. You should read both this prospectus and any accompanying prospectus supplement together with the additional information described under the heading "Where You Can Find More Information" beginning on page 27 of this prospectus.

You should rely only on the information contained in or incorporated by reference in this prospectus, the accompanying prospectus supplement or in any related free writing prospectus filed by us with the SEC. We have not authorized anyone to provide you with different information. This prospectus and the accompanying prospectus supplement do not constitute an offer to sell or the solicitation of an offer to buy any securities other than the securities described in the accompanying prospectus supplement or an offer to sell or the solicitation of an offer to buy such securities in any circumstances in which such offer or solicitation is unlawful. You should assume that the information appearing in this prospectus, any prospectus supplement, the documents incorporated by reference and any related free writing prospectus is accurate only as of their respective dates. Our business, financial condition, results of operations and prospects may have changed materially since those dates.

**Unless the context otherwise requires, references to "Altimmune," the "Company," "we," "us" and "our" refer to Altimmune, Inc., and its wholly owned, consolidated subsidiaries, or either or all of them as the context may require.**

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#### RISK FACTORS
Investing in our securities involves a high degree of risk. You should carefully consider the risks described in the documents incorporated by reference in this prospectus and any prospectus supplement, as well as other information we include or incorporate by reference into this prospectus and any applicable prospectus supplement, before making an investment decision. Our business, financial condition or results of operations could be materially and adversely affected by the materialization of any of these risks. The trading price of our securities could decline due to the materialization of any of these risks, and you may lose all or part of your investment. This prospectus and the documents incorporated herein by reference also contain forward-looking statements that involve risks and uncertainties. Actual results could differ materially from those anticipated in these forward-looking statements as a result of certain factors, including the risks described in the documents incorporated herein by reference, including (i) our most recent Annual Report on Form 10-K, which is on file with the SEC and is incorporated herein by reference, and (ii) other documents we file with the SEC that are deemed incorporated by reference into this prospectus, including our Quarterly Reports on Form 10-Q.

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#### CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS
This prospectus, any applicable prospectus supplement, any related free writing prospectus, and the information incorporated by reference herein and therein contain express or implied statements that are based on our management's belief and assumptions and on information currently available to our management are considered forward-looking within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act. All statements other than statements of historical facts are forward-looking statements, including statements regarding our future results of operations or of our financial position, business strategy, plans and objectives of management for future operations, or state other forward-looking information. In some cases, you can identify these statements by forward-looking words such as "anticipate," "believe," "contemplate," "continue," "could," "estimate," "expect," "intend," "may," "plan," "potential," "predict," "project," "should," "target," "will," or "would" or the negative of these words or other similar terms or expressions. We believe that it is important to communicate our future expectations to our investors. However, there may be events in the future that we are not able to accurately predict or control and that may cause our actual results to differ materially from the expectations we describe in our forward-looking statements.

These forward-looking statements are neither promises nor guarantees of future performance and relate to future events or our future operational or financial performance, and involve known and unknown risks, uncertainties, and other factors, many of which are beyond our control, that may cause our actual results, performance, or achievements to be materially different from any future results, performance, or achievements expressed or implied by these forward-looking statements, including, without limitation the risk factors and cautionary statements described in other documents that we file from time to time with the SEC, specifically under "Item 1A. Risk Factors" and elsewhere in our most recent Annual Report on Form 10-K and the section of any accompanying prospectus supplement entitled "Risk Factors," as may be updated by our subsequent Quarterly Reports on Form 10-Q and other filings we make with the SEC.

Given these uncertainties, you should not place undue reliance on these forward-looking statements. These forward-looking statements speak only as of the date on which the statements were made and are not guarantees of future performance. Except as may be required by applicable law, we do not undertake or intend to update any forward-looking statements after the date of this prospectus or the respective dates of documents incorporated by reference herein that include forward-looking statements.

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#### OUR COMPANY
**Our Business**

**Overview**

Altimmune, Inc. is a late clinical-stage biopharmaceutical company developing novel peptide-based therapeutics for liver and cardiometabolic diseases. Our lead program is pemvidutide (formerly known as ALT-801), a balanced 1:1 glucagon/GLP-1 dual receptor agonist for the treatment of metabolic associated steatohepatitis ("MASH"), alcohol use disorder ("AUD") and alcohol-associated liver disease ("ALD"). We may also pursue additional indications for pemvidutide that leverage our differentiated clinical profile.

**Recent Developments**

*Completion of Enrollment in RECLAIM Phase 2 Trial*

On November 3, 2025, we announced early completion of enrollment in the RECLAIM Phase 2 Trial evaluating Pemvidutide in AUD. Enrollment completed ahead of schedule, underscoring strong interest from patient community in a new therapeutic option for AUD. We noted that we are on track to complete the 24-week treatment period and announce topline results in 2026.

*Amendment to Hercules Loan and Security Agreement*

On November 5, 2025, (the "Amendment Closing"), the Company entered into an amendment to the Loan and Security Agreement with Hercules Capital, Inc. and the lenders party thereto, pursuant to which the lenders will make available up to four tranches of term loans (the "Term Loan"), subject to certain terms and conditions that, among others, increase the availability under the Term Loan from an aggregate principal amount of $100.0 million to $125.0 million. The Term Loan, as amended, is structured in four tranches. The first Term Loan tranche was drawn down at closing on May 13, 2025 in an aggregate principal amount of $15.0 million. The second Term Loan tranche was drawn down on the Amendment Closing in an aggregate principal amount of $20.0 million. Upon the achievement of certain milestones and subject to other terms and conditions set out in the Loan Agreement, as amended, the third Term Loan tranche will be made available in an aggregate principal amount of up to $10.0 million. The fourth Term Loan tranche will be made available in an aggregate principal amount of up to $80.0 million subject to the approval of the lenders. The Term Loan, as amended, bears interest equal to the greater of (a) 9.70% per annum and (b) the prime rate as reported in The Wall Street Journal plus 2.45% per annum. The interest-only period has been extended to 30 months from May 13, 2025.

*Entry into November 2025 ATM Program and Termination of February 2025 ATM Program*

On November 6, 2025, we entered an Equity Distribution Agreement (the "November 2025 Agreement") with Leerink Partners LLC serving as the sales agent, with respect to an at-the-market offerings program under which we may offer and sell shares of our common stock having an aggregate offering price of up to $200.0 million through the sales agent (the "November 2025 ATM"). All Shares offered and sold in the November 2025 ATM will be issued pursuant to the Company's Registration Statement on Form S-3 filed with the SEC on February 27, 2025, which was declared effective on March 13, 2025.

Prior to entering the November 2025 Agreement, the Company provided notice to Leerink Partners LLC, Piper Sandler & Co. and Stifel, Nicolaus & Company, Incorporated (the "February Sales Agents"), to terminate the Equity Distribution Agreement entered into with the February Sales Agents on February 27, 2025 (the "February 2025 Agreement"). The Company is not subject to any termination penalties related to the termination of the February 2025 Agreement. As of September 30, 2025, the Company had sold 18,524,709 shares of common stock under the February 2025 Agreement resulting in approximately $81.9 million in net proceeds, and as of September 30, 2025, $65.4 million remained available to be sold under the 2025 Agreement.

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**Corporate History**

We were incorporated in Delaware in April 2005 and subsequently changed our name to Altimmune, Inc. in May 2017 upon the completion of our merger with PharmAthene, Inc. Our principal executive offices are located at 910 Clopper Road, Suite 201S, Gaithersburg, Maryland 20878, and our telephone number is (240) 654-1450. Our Internet website is www.altimmune.com and our investor relations website is located under the "Investors" tab. The information contained on, or that can be accessed through, our website is not a part of this prospectus. We have included our website address in this prospectus solely as an inactive textual reference.

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#### USE OF PROCEEDS
We intend to use the net proceeds from the sale of any securities offered under this prospectus for general corporate purposes unless otherwise indicated in the applicable prospectus supplement. General corporate purposes may include, but are not limited to research and clinical development of current or additional pipeline candidates, working capital, capital expenditures and other general corporate purposes. We may temporarily invest the net proceeds in a variety of capital preservation instruments, including short-term, investment-grade, interest-bearing instruments and U.S. government securities, or may hold such proceeds as cash, until they are used for their stated purpose. We have not determined the amount of net proceeds to be used specifically for such purposes. As a result, management will retain broad discretion over the allocation of net proceeds.

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#### SECURITIES WE MAY OFFER OR SELL
This prospectus contains summary descriptions of the securities we may offer or sell from time to time. These summary descriptions are not meant to be complete descriptions of each security. The particular terms of any security will be described in the applicable prospectus supplement. This prospectus provides you with a general description of the securities we may offer. Each time we sell securities described herein, we will provide prospective investors with a supplement to this prospectus that will contain specific information about the terms of that offering, including the specific amounts, prices and terms of the securities offered.

We may sell the securities to or through underwriters, dealers or agents, directly to purchasers or through a combination of any of these methods of sale or as otherwise set forth below under "Plan of Distribution." We, as well as any agents acting on our behalf, reserve the sole right to accept and to reject in whole or in part any proposed purchase of securities. Any prospectus supplement will set forth the names of any underwriters, dealers, agents or other entities involved in the sale of securities described in that prospectus supplement and any applicable fee, commission or discount arrangements with them.

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#### DESCRIPTION OF CAPITAL STOCK
*The following description of our common stock and preferred stock, together with the additional information we include in any applicable prospectus supplements, summarizes the material terms and provisions of the common stock and preferred stock that we may offer under this prospectus. The following description of our capital stock does not purport to be complete and is subject to, and qualified in its entirety by, our certificate of incorporation and bylaws, which are exhibits to the registration statement of which this prospectus forms a part, and by applicable law. The terms of our common stock and preferred stock may also be affected by Delaware law.*

**General**

Under our charter, our authorized capital stock consists of two hundred million (200,000,000) shares of common stock, par value $0.0001 per share, and one million (1,000,000) shares of undesignated preferred stock, par value $0.0001 per share.

**Common Stock**

Under our Amended and Restated Certificate of Incorporation, as amended, to which we refer as our "charter," we are currently authorized to issue 200,000,000 shares of common stock, par value $0.0001 per share. As of November 5, 2025, we had 104,342,385 shares of common stock outstanding.

Holders of our common stock are entitled to one vote for each share of common stock held of record on all matters to be voted on by stockholders, except as otherwise provided by law or in any preferred stock designation. Our bylaws specify that, except as otherwise required by law or our charter, the presence in person or by proxy of holders of a majority of the shares entitled to vote at a meeting of stockholders will be necessary, and will constitute a quorum, for the transaction of business at such meeting. Our bylaws furthermore specify that all elections of directors will be determined by a plurality of the votes and that, except as otherwise provided by law or in the charter or bylaws, any other matter will be determined by the vote of a majority of the shares which are voted with regard to it. Holders of our common stock have no conversion, preemptive or other subscription rights and there are no sinking fund or redemption provisions applicable to the common stock.

There is no cumulative voting with respect to the election of directors, with the result that the holders of more than 50% of the shares voting for the election of directors can elect all of the directors then up for election. Holders of our common stock are entitled to receive dividends when, as and if declared by our board of directors out of funds legally available therefor. In the event of our liquidation, dissolution or winding up, the holders of common stock are entitled to share in all assets remaining which are available for distribution to them after payment of liabilities and after provision has been made for each class of stock, if any, having preference over the common stock.

Our common stock is listed on The Nasdaq Global Select Market under the trading symbol "ALT".

***Annual Meeting***

Annual meetings of our stockholders are held on the date designated in accordance with our amended and restated by-laws. Written notice must be mailed to each stockholder entitled to vote not less than ten nor more than 60 days before the date of the meeting. The presence in person or by proxy of the holders of record of a majority of our issued and outstanding shares entitled to vote at such meeting constitutes a quorum for the transaction of business at meetings of the stockholders. Special meetings of the stockholders may be called for any purpose only by the board of directors pursuant to a resolution approved by the affirmative vote of a majority of the directors then in office. Except as may be otherwise provided by applicable law, our certificate of incorporation or our amended and restated by-laws, all elections of directors shall be decided by a plurality, and all other questions shall be decided by a majority, of the votes cast by stockholders entitled to vote thereon at a duly held meeting of stockholders at which a quorum is present.

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***Voting Rights***

Holders of common stock are entitled to one vote for each share held of record on all matters to be voted upon by stockholders and do not have cumulative voting rights.

***Dividends***

Subject to the rights, powers and preferences of any outstanding preferred stock that we may designate and issue in the future, and except as provided by law or in our certificate of incorporation, dividends may be declared and paid or set aside for payment on the Common Stock out of legally available assets or funds when and as declared by our board of directors.

***Liquidation, Dissolution and Winding Up***

Subject to the rights, powers and preferences of any outstanding preferred stock that we may designate and issue in the future, in the event of our liquidation, dissolution or winding up, our net assets will be distributed pro rata to the holders of Common Stock.

***Other Rights***

Holders of Common Stock have no preemptive, subscription, redemption or conversion rights. The rights, preferences and privileges of holders of Common Stock are subject to and may be adversely affected by the rights of the holders of shares of any series of preferred stock that we may designate and issue in the future. Holders of Common Stock are not required to make additional capital contributions.

***Transfer Agent***

The transfer agent and registrar for the common stock is Continental Stock Transfer & Trust Company, New York, New York.

**Preferred Stock**

Under our charter, we are currently authorized to issue 1,000,000 shares of preferred stock, par value $.0001 per share. As of September 30, 2025, we had no shares of preferred stock issued and outstanding.

Under our charter, our board of directors is expressly granted authority to issue shares of preferred stock, in one or more series, and to fix for each series such voting powers, full or limited, and such designations, preferences and relative, participating, optional or other special rights and such qualifications, limitations or restrictions as it may determine in the resolution or resolutions providing for the issue of such series (to which we also refer as a "preferred stock designation") and as may be permitted by the Delaware General Corporation Law. The number of authorized shares of preferred stock may be increased or decreased (but not below the number of shares of preferred stock then outstanding) by the affirmative vote of the holders of a majority of the voting power of all of the then outstanding shares of our capital stock entitled to vote generally in the election of directors, voting together as a single class, without a separate vote of the holders of the preferred stock, or any series of preferred stock, unless a vote of any such holders is required pursuant to any preferred stock designation.

The rights and terms relating to any new series of preferred stock could adversely affect the voting power or other rights of the holders of the common stock or could be utilized, under certain circumstances, as a method of discouraging, delaying or preventing a change in control of the Company.

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**Provisions of Our Certificate of Incorporation and Amended and Restated By-laws and Delaware Law That May Have Anti-Takeover Effects**

The provisions of Delaware law and our certificate of incorporation and amended and restated by-laws could discourage or make it more difficult to accomplish a proxy contest or other change in our management or the acquisition of control by a holder of a substantial amount of our voting stock. It is possible that these provisions could make it more difficult to accomplish, or could deter, transactions that stockholders may otherwise consider to be in their best interests or in our best interests. These provisions are intended to enhance the likelihood of continuity and stability in the composition of our board of directors and in the policies formulated by the board of directors and to discourage certain types of transactions that may involve an actual or threatened change of our control. These provisions are designed to reduce our vulnerability to an unsolicited acquisition proposal and to discourage certain tactics that may be used in proxy fights. Such provisions also may have the effect of preventing changes in our management.

***Removal of Directors by Stockholders***

Our amended and restated bylaws provide that members of our board of directors may only be removed for cause by a vote of the holders of a majority of the voting power of the outstanding shares entitled to vote on the election of the directors, voting together as a single class.

***Issuance of Preferred Stock***

Our board of directors is authorized, without further action by our stockholders, to issue up to 1,000,000 shares of preferred stock in one or more series, and to fix the designations, powers, preferences and the relative, participating, optional or other special rights, and any qualifications, limitations and restrictions of the shares of each series of preferred stock. The issuance of preferred stock could impede the completion of a merger, tender offer or other takeover attempt.

***Stockholder Nomination of Directors***

Our amended and restated bylaws provide that a stockholder must notify us in writing of any stockholder nomination of a director not earlier than 5:00 p.m., Eastern Time, on the 120th day and not later than 5:00 p.m., Eastern Time, on the 90th day prior to the first anniversary of the preceding year's annual meeting; provided, that if there was no annual meeting in the prior year or if the date of the current year's annual meeting is more than 30 days before or after the anniversary date of the prior year's annual meeting, notice by the stockholder to be timely must be so delivered on or before 10 days after the day on which the date of the current year's annual meeting is first disclosed in a public announcement by us.

***No Action By Written Consent***

Our certificate of incorporation provides that our stockholders may not act by written consent and may only act at duly called meetings of stockholders.

***Delaware Business Combination Statute***

Section 203 of the General Corporation Law of the State of Delaware, which we refer to as the DGCL, is applicable to us. Section 203 of the DGCL restricts some types of transactions and business combinations between a corporation and a 15% stockholder. A 15% stockholder is generally considered by Section 203 to be a person owning 15% or more of the corporation's outstanding voting stock. Section 203 refers to a 15% stockholder as an "interested stockholder." Section 203 restricts these transactions for a period of three years from the date the stockholder acquires 15% or more of our outstanding voting stock. With some exceptions, unless the transaction is approved by the board of directors and the holders of at least two-thirds of the outstanding voting stock of the corporation, Section 203 prohibits significant business transactions such as:

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● a merger with, disposition of significant assets to or receipt of disproportionate financial benefits by the interested stockholder, and

● any other transaction that would increase the interested stockholder's proportionate ownership of any class or series of our capital stock.

The shares held by the interested stockholder are not counted as outstanding when calculating the two-thirds of the outstanding voting stock needed for approval.

The prohibition does not apply if:

● prior to the time that any stockholder became an interested stockholder, the board of directors approved either the business combination or the transaction in which such stockholder acquired 15% or more of our outstanding voting stock, or

● the interested stockholder owns at least 75% of our outstanding voting stock as a result of a transaction in which such stockholder acquired 15% or more of our outstanding voting stock. Shares held by persons who are both directors and officers or by some types of employee stock plans are not counted as outstanding when making this calculation.

***Choice of forum***

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#### DESCRIPTION OF DEBT SECURITIES
We may offer debt securities that may be senior or subordinated. We refer to senior debt securities and subordinated debt securities collectively as debt securities. Each series of debt securities may have different terms. The following description summarizes the general terms and provisions of the debt securities we might issue. We will describe the specific terms of the debt securities we offer for sale and the extent, if any, to which the general provisions summarized below apply to any series of debt securities in the prospectus supplement relating to the series and any applicable free writing prospectus that we authorize to be delivered.

We may issue senior debt securities from time to time, in one or more series under a senior indenture to be entered into between us and a senior trustee to be named in a prospectus supplement, which we refer to as the senior trustee. We may issue subordinated debt securities from time to time, in one or more series, under a subordinated indenture to be entered into between us and a subordinated trustee to be named in a prospectus supplement, which we refer to as the subordinated trustee. The forms of senior indenture and subordinated indenture are filed as exhibits to the registration statement of which this prospectus forms a part. Together, the senior indenture and the subordinated indenture are referred to as the indentures and, together, the senior trustee and the subordinated trustee are referred to as the trustees. This prospectus briefly outlines some of the provisions of the indentures. The following summary of the material provisions of the indentures is qualified in its entirety by the provisions of the indentures, including definitions of certain terms used in the indentures. Wherever we refer to particular sections or defined terms of the indentures, those sections or defined terms are incorporated by reference in this prospectus or the applicable prospectus supplement. You should review the indentures that are filed as exhibits to the registration statement of which this prospectus forms a part for additional information. As used in this prospectus, the term "debt securities" includes the debt securities being offered by this prospectus and all other debt securities issued by us under the indentures.

#### General
The indentures:

● do not limit the amount of debt securities that we may issue;

● allow us to issue debt securities in one or more series;

● do not require us to issue all of the debt securities of a series at the same time; and

● allow us to reopen a series to issue additional debt securities without the consent of the holders of the debt securities of such series.

Unless otherwise provided in the applicable prospectus supplement, the senior debt securities will be unsubordinated obligations and will rank equally with all of our other unsecured and unsubordinated indebtedness. Payments on the subordinated debt securities will be subordinated to the prior payment in full of all of our senior indebtedness, as described under "Subordination" and in the applicable prospectus supplement.

Each indenture provides that we may, but need not, designate more than one trustee under an indenture. Any trustee under an indenture may resign or be removed and a successor trustee may be appointed to act with respect to the series of debt securities administered by the resigning or removed trustee. If two or more persons are acting as trustee with respect to different series of debt securities, each trustee shall be a trustee of a trust under the applicable indenture separate and apart from the trust administered by any other trustee. Except as otherwise indicated in this prospectus, any action described in this prospectus to be taken by each trustee may be taken by each trustee with respect to, and only with respect to, the one or more series of debt securities for which it is trustee under the applicable indenture.

The prospectus supplement for each offering will provide the following terms, where applicable:

● the title of the debt securities and whether they are senior or subordinated;

● any limit upon the aggregate principal amount of the debt securities of that series;

● the date or dates on which the principal of the debt securities of the series is payable;

● the price at which the debt securities will be issued, expressed as a percentage of the principal and, if other than the principal amount thereof, the portion of the principal amount thereof payable upon declaration of acceleration of the maturity thereof or, if applicable, the portion of the principal amount of such debt securities that is convertible into another security of ours or the method by which any such portion shall be determined;

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● the rate or rates at which the debt securities of the series shall bear interest or the manner of calculation of such rate or rates, if any;

● the date or dates from which interest will accrue, the interest payment dates on which such interest will be payable or the manner of determination of such interest payment dates, the place(s) of payment, and the record date for the determination of holders to whom interest is payable on any such interest payment dates or the manner of determination of such record dates;

● the right, if any, to extend the interest payment periods and the duration of such extension;

● the period or periods within which, the price or prices at which and the terms and conditions upon which debt securities of the series may be redeemed, converted or exchanged, in whole or in part;

● our obligation, if any, to redeem or purchase debt securities of the series pursuant to any sinking fund, mandatory redemption, or analogous provisions (including payments made in cash in satisfaction of future sinking fund obligations) or at the option of a holder thereof and the period or periods within which, the price or prices at which, and the terms and conditions upon which, debt securities of the series shall be redeemed or purchased, in whole or in part, pursuant to such obligation;

● the form of the debt securities of the series including the form of the Certificate of Authentication for such series;

● if other than minimum denominations of one thousand U.S. dollars ($1,000) or any integral multiple of $1,000 thereof, the denominations in which the debt securities of the series shall be issuable;

● whether the debt securities of the series shall be issued in whole or in part in the form of a global debt security or global debt securities; the terms and conditions, if any, upon which such global debt security or global debt securities may be exchanged in whole or in part for other individual debt securities; and the depositary for such global debt security or global debt securities;

● whether the debt securities will be convertible into or exchangeable for common stock or other securities of ours or any other Person and, if so, the terms and conditions upon which such debt securities will be so convertible or exchangeable, including the conversion or exchange price, as applicable, or how it will be calculated and may be adjusted, any mandatory or optional (at our option or the holders' option) conversion or exchange features, and the applicable conversion or exchange period;

● any additional or alternative events of default to those set forth in the indenture;

● any additional or alternative covenants to those set forth in the indenture;

● the currency or currencies including composite currencies, in which payment of the principal of (and premium, if any) and interest, if any, on such debt securities shall be payable (if other than the currency of the United States of America), which unless otherwise specified shall be the currency of the United States of America as at the time of payment is legal tender for payment of public or private debts;

● if the principal of (and premium, if any), or interest, if any, on such debt securities is to be payable, at our election or at the election of any holder thereof, in a coin or currency other than that in which such debt securities are stated to be payable, then the period or periods within which, and the terms and conditions upon which, such election may be made;

● whether interest will be payable in cash or additional debt securities at our or the holders' option and the terms and conditions upon which the election may be made;

● the terms and conditions, if any, upon which we will pay amounts in addition to the stated interest, premium, if any and principal amounts of the debt securities of the series to any holder that is not a "United States person" for federal tax purposes;

● additional or alternative provisions, if any, related to defeasance and discharge of the offered debt securities than those set forth in the indenture;

● the applicability of any guarantees;

● any restrictions on transfer, sale or assignment of the debt securities of the series; and

● any other terms of the debt securities (which may supplement, modify or delete any provision of the indenture insofar as it applies to such series).

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We may issue debt securities that provide for less than the entire principal amount thereof to be payable upon declaration of acceleration of the maturity of the debt securities. We refer to any such debt securities throughout this prospectus as "original issue discount securities."

We will provide you with more information in the applicable prospectus supplement regarding any deletions, modifications, or additions to the events of default or covenants that are described below, including any addition of a covenant or other provision providing event risk or similar protection.

#### Payment
Unless otherwise provided in the applicable prospectus supplement, the principal of, and any premium or make-whole amount, and interest on, any series of the debt securities will be payable by mailing a check to the address of the person entitled to it as it appears in the applicable register for the debt securities or by wire transfer of funds to that person at an account maintained within the United States.

All monies that we pay to a paying agent or a trustee for the payment of the principal of, and any premium, or interest on, any debt security will be repaid to us if unclaimed at the end of two years after the obligation underlying payment becomes due and payable. After funds have been returned to us, the holder of the debt security may look only to us for payment, without payment of interest for the period which we hold the funds.

#### Merger, Consolidation or Sale of Assets
The indentures provide that we may, without the consent of the holders of any outstanding debt securities, (i) consolidate with, (ii) sell, lease or convey all or substantially all of our assets to, or (iii) merge with or into, any other entity, provided that:

● either we are the continuing entity, or the successor entity, if other than us, assumes the obligations (a) to pay the principal of, and any premium, and interest on, all of the debt securities and (b) to duly perform and observe all of the covenants and conditions contained in the applicable indenture; and in the event the debt securities are convertible into or exchangeable for common stock or other securities of ours, such successor entity will, by such supplemental indenture, make provision so that the holders of debt securities of that series shall thereafter be entitled to receive upon conversion or exchange of such debt securities the number of securities or property to which a holder of the number of common stock or other securities of ours deliverable upon conversion or exchange of those debt securities would have been entitled had such conversion or exchange occurred immediately prior to such consolidation, merger, sale, conveyance, transfer or other disposition; and

● an officers' certificate and legal opinion covering such conditions are delivered to each applicable trustee.

**Events of Default, Notice and Waiver**

Unless the applicable prospectus supplement states otherwise, when we refer to "events of default" as defined in the indentures with respect to any series of debt securities, we mean:

● default in the payment of any installment of interest on any debt security of such series continuing for 90 days unless such date has been extended or deferred;

● default in the payment of principal of, or any premium on, any debt security of such series when due and payable unless such date has been extended or deferred;

● default in the performance or breach of any covenant or warranty in the debt securities or in the indenture by us continuing for 90 days after written notice described below;

● bankruptcy insolvency or reorganization, or court appointment of a receiver, liquidator or trustee of us; and

● any other event of default provided with respect to a particular series of debt securities.

If an event of default (other than an event of default described in the fourth bullet point above) occurs and is continuing with respect to debt securities of any series outstanding, then the applicable trustee or the holders of 25% or more in principal amount of the debt securities of that series will have the right to declare the principal amount of, and accrued interest on, all the debt securities of that series to be due and payable. If an event of default described in the fourth bullet point above occurs, the principal amount of, and accrued interest on, all the debt securities of that series will

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automatically become and will be immediately due and payable without any declaration or other act on the part of the trustee or the holders of the debt securities. However, at any time after such a declaration of acceleration has been made, but before a judgment or decree for payment of the money due has been obtained by the applicable trustee, the holders of at least a majority in principal amount of outstanding debt securities of such series or of all debt securities then outstanding under the applicable indenture may rescind and annul such declaration and its consequences if:

● we have deposited with the applicable trustee all required payments of the principal, any premium, interest and, to the extent permitted by law, interest on overdue installment of interest, plus applicable fees, expenses, disbursements and advances of the applicable trustee; and

● all events of default, other than the non-payment of accelerated principal, or a specified portion thereof, and any premium, have been cured or waived.

The indentures provide that holders of debt securities of any series may not institute any proceedings, judicial or otherwise, with respect to such indenture or for any remedy under the indenture, unless the trustee fails to act for a period of 90 days after the trustee has received a written request to institute proceedings in respect of an event of default from the holders of 25% or more in principal amount of the outstanding debt securities of such series, as well as an offer of indemnity reasonably satisfactory to the trustee. However, this provision will not prevent any holder of debt securities from instituting suit for the enforcement of payment of the principal of, and any premium, and interest on, such debt securities at the respective due dates thereof.

The indentures provide that, subject to provisions in each indenture relating to its duties in the case of a default, a trustee has no obligation to exercise any of its rights or powers at the request or direction of any holders of any series of debt securities then outstanding under the indenture, unless the holders have offered to the trustee reasonable security or indemnity. The holders of at least a majority in principal amount of the outstanding debt securities of any series or of all debt securities then outstanding under an indenture shall have the right to direct the time, method and place of conducting any proceeding for any remedy available to the applicable trustee, or of exercising any trust or power conferred upon such trustee. However, a trustee may refuse to follow any direction which:

● is in conflict with any law or the applicable indenture;

● may involve the trustee in personal liability; or

● may be unduly prejudicial to the holders of debt securities of the series not joining the proceeding.

Within 120 days after the close of each fiscal year, we will be required to deliver to each trustee a certificate, signed by one of our several specified officers, stating whether or not that officer has knowledge of any default under the applicable indenture. If the officer has knowledge of any default, the notice must specify the nature and status of the default.

#### Modification of the Indentures
Subject to certain exceptions, the indentures may be amended with the consent of the holders of a majority in aggregate principal amount of the outstanding debt securities of all series affected by such amendment (including consents obtained in connection with a tender offer or exchange for the debt securities of such series).

We and the applicable trustee may make modifications and amendments of an indenture without the consent of any holder of debt securities for any of the following purposes:

● to cure any ambiguity, defect, or inconsistency in the applicable indenture or in the Securities of any series;

● to comply with the covenant described above under "Merger, Consolidation or Sale of Assets;"

● to provide for uncertificated debt securities in addition to or in place of certificated debt securities;

● to add events of default for the benefit of the holders of all or any series of debt securities;

● to add the covenants, restrictions, conditions or provisions relating to us for the benefit of the holders of all or any series of debt securities (and if such covenants, restrictions, conditions or provisions are to be for the benefit of less than all series of debt securities, stating that such covenants, restrictions, conditions or provisions are expressly being included solely for the benefit of such series), to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default, or to surrender any right or power in the applicable indenture conferred upon us;

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● to add to, delete from, or revise the conditions, limitations, and restrictions on the authorized amount, terms, or purposes of issue, authentication, and delivery of debt securities, as set forth in the applicable indenture;

● to make any change that does not adversely affect the rights of any holder of notes under the applicable indenture in any material respect;

● to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided in the applicable indenture, to establish the form of any certifications required to be furnished pursuant to the terms of the applicable indenture or any series of debt securities under the applicable indenture, or to add to the rights of the holders of any series of debt securities;

● to evidence and provide for the acceptance of appointment under the applicable indenture by a successor trustee or to appoint a separate trustee with respect to any series;

● to comply with any requirements of the SEC or any successor in connection with the qualification of the indenture under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act; or

● to conform the applicable indenture to this "Description of Debt Securities" or any other similarly titled section in any prospectus supplement or other offering document relating to a series of debt securities.

**Subordination**

Payment by us of the principal of, premium, if any, and interest on any series of subordinated debt securities issued under the subordinated indenture will be subordinated to the extent set forth in an indenture supplemental to the subordinated indenture relating to such series.

#### Discharge, Defeasance and Covenant Defeasance
Unless otherwise provided in the applicable prospectus supplement, the indentures allow us to discharge our obligations to holders of any series of debt securities issued under any indenture when:

● either (i) all securities of such series have already been delivered to the applicable trustee for cancellation; or (ii) all securities of such series have not already been delivered to the applicable trustee for cancellation but (a) have become due and payable, (b) will become due and payable within one year, or (c) if redeemable at our option, are to be redeemed within one year, and we have irrevocably deposited with the applicable trustee, in trust, funds in such currency or currencies, or governmental obligations in an amount sufficient to pay the entire indebtedness on such debt securities in respect of principal and any premium, and interest to the date of such deposit if such debt securities have become due and payable or, if they have not, to the stated maturity or redemption date; and

● we have paid or caused to be paid all other sums payable.

Unless otherwise provided in the applicable prospectus supplement, the indentures provide that, upon our irrevocable deposit with the applicable trustee, in trust, of an amount, in such currency or currencies in which such debt securities are payable at stated maturity, or government obligations, or both, applicable to such debt securities, which through the scheduled payment of principal and interest in accordance with their terms will provide money in an amount sufficient to pay the principal of, and any premium or make-whole amount, and interest on, such debt securities, and any mandatory sinking fund or analogous payments thereon, on the scheduled due dates therefor, the issuing company shall be released from its obligations with respect to such debt securities under the applicable indenture or, if provided in the applicable prospectus supplement, its obligations with respect to any other covenant, and any omission to comply with such obligations shall not constitute an event of default with respect to such debt securities.

The applicable prospectus supplement may further describe the provisions, if any, permitting such defeasance or covenant defeasance, including any modifications to the provisions described above, with respect to the debt securities of or within a particular series.

#### Conversion Rights
The terms and conditions, if any, upon which the debt securities are convertible into common stock or other securities of ours will be set forth in the applicable prospectus supplement. The terms will include whether the debt securities are convertible into shares of common stock or other securities of ours, the conversion price, or manner of calculation

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thereof, the conversion period, provisions as to whether conversion will be at the issuing company's option or the option of the holders, the events requiring an adjustment of the conversion price and provisions affecting conversion in the event of the redemption of the debt securities and any restrictions on conversion.

#### Governing Law
The indentures and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

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#### DESCRIPTION OF WARRANTS
The following description, together with the additional information we may include in any applicable prospectus supplements, summarizes the material terms and provisions of the warrants that we may offer under this prospectus and the related warrant agreements and warrant certificates. While the terms summarized below will apply generally to any warrants that we may offer, we will describe the particular terms of any series of warrants in more detail in the applicable prospectus supplement. If we indicate in the applicable prospectus supplement, the terms of any warrants offered under that prospectus supplement may differ from the terms described below. Specific warrant agreements will contain additional important terms and provisions and will be incorporated by reference as an exhibit to the registration statement, which includes this prospectus.

#### General
We may issue warrants for the purchase of common stock, preferred stock and/or debt securities in one or more series. We may issue warrants independently or together with common stock, preferred stock and/or debt securities, and the warrants may be attached to or separate from these securities.

We will evidence each series of warrants by warrant certificates that we will issue under a separate warrant agreement. We will enter into the warrant agreement with a warrant agent. We will indicate the name and address of the warrant agent in the applicable prospectus supplement relating to a particular series of warrants.

We will describe in the applicable prospectus supplement the terms of the series of warrants, including:

● the offering price and aggregate number of warrants offered;

● the currency for which the warrants may be purchased;

● if applicable, the designation and terms of the securities with which the warrants are issued and the number of warrants issued with each such security or each principal amount of such security;

● if applicable, the date on and after which the warrants and the related securities will be separately transferable;

● in the case of warrants to purchase debt securities, the principal amount of debt securities purchasable upon exercise of one warrant and the price at, and currency in which, this principal amount of debt securities may be purchased upon such exercise;

● in the case of warrants to purchase common stock or preferred stock, the number of shares of common stock or preferred stock, as the case may be, purchasable upon the exercise of one warrant and the price at which these shares may be purchased upon such exercise;

● the effect of any merger, consolidation, sale or other disposition of our business on the warrant agreement and the warrants;

● the terms of any rights to redeem or call the warrants;

● any provisions for changes to or adjustments in the exercise price or number of securities issuable upon exercise of the warrants;

● the periods during which, and places at which, the warrants are exercisable;

● the manner of exercise;

● the dates on which the right to exercise the warrants will commence and expire;

● the manner in which the warrant agreement and warrants may be modified;

● federal income tax consequences of holding or exercising the warrants;

● the terms of the securities issuable upon exercise of the warrants; and

● any other specific terms, preferences, rights or limitations of or restrictions on the warrants.

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#### DESCRIPTION OF UNITS
We may issue units comprised of shares of common stock, shares of preferred stock, debt securities and warrants in any combination. We may issue units in such amounts and in as many distinct series as we wish. This section outlines certain provisions of the units that we may issue. If we issue units, they will be issued under one or more unit agreements to be entered into between us and a bank or other financial institution, as unit agent. The information described in this section may not be complete in all respects and is qualified entirely by reference to the unit agreement with respect to the units of any particular series. The specific terms of any series of units offered will be described in the applicable prospectus supplement. If so described in a particular prospectus supplement, the specific terms of any series of units may differ from the general description of terms presented below. We urge you to read any prospectus supplement related to any series of units we may offer, as well as the complete unit agreement and unit certificate that contain the terms of the units. If we issue units, forms of unit agreements and unit certificates relating to such units will be incorporated by reference as exhibits to the registration statement, which includes this prospectus.

Each unit that we may issue will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately, at any time or at any time before a specified date. The applicable prospectus supplement may describe:

● the designation and terms of the units and of the securities comprising the units, including whether and under what circumstances those securities may be held or transferred separately;

● any provisions of the governing unit agreement;

● the price or prices at which such units will be issued;

● the applicable United States federal income tax considerations relating to the units;

● any provisions for the issuance, payment, settlement, transfer or exchange of the units or of the securities comprising the units; and

● any other terms of the units and of the securities comprising the units.

The provisions described in this section, as well as those described under "Description of Capital Stock," "Description of Debt Securities" and "Description of Warrants" will apply to the securities included in each unit, to the extent relevant and as may be updated in any prospectus supplements.

**Issuance in Series**

We may issue units in such amounts and in as many distinct series as we wish. This section summarizes terms of the units that apply generally to all series. Most of the financial and other specific terms of a particular series of units will be described in the applicable prospectus supplement.

**Unit Agreements**

We will issue the units under one or more unit agreements to be entered into between us and a bank or other financial institution, as unit agent. We may add, replace or terminate unit agents from time to time. We will identify the unit agreement under which each series of units will be issued and the unit agent under that agreement in the applicable prospectus supplement.

The following provisions will generally apply to all unit agreements unless otherwise stated in the applicable prospectus supplement:

#### Modification without Consent
We and the applicable unit agent may amend any unit or unit agreement without the consent of any holder:

● to cure any ambiguity, including modifying any provisions of the governing unit agreement that differ from those described below;

● to correct or supplement any defective or inconsistent provision; or

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● to make any other change that we believe is necessary or desirable and will not adversely affect the interests of the affected holders in any material respect.

We do not need any approval to make changes that affect only units to be issued after the changes take effect. We may also make changes that do not adversely affect a particular unit in any material respect, even if they adversely affect other units in a material respect. In those cases, we do not need to obtain the approval of the holder of the unaffected unit; we need only obtain any required approvals from the holders of the affected units.

#### Modification with Consent
We may not amend any particular unit or a unit agreement with respect to any particular unit unless we obtain the consent of the holder of that unit, if the amendment would:

● impair any right of the holder to exercise or enforce any right under a security included in the unit if the terms of that security require the consent of the holder to any changes that would impair the exercise or enforcement of that right; or

● reduce the percentage of outstanding units or any series or class the consent of whose holders is required to amend that series or class, or the applicable unit agreement with respect to that series or class, as described below.

Any other change to a particular unit agreement and the units issued under that agreement would require the following approval:

● if the change affects only the units of a particular series issued under that agreement, the change must be approved by the holders of a majority of the outstanding units of that series; or

● if the change affects the units of more than one series issued under that agreement, it must be approved by the holders of a majority of all outstanding units of all series affected by the change, with the units of all the affected series voting together as one class for this purpose.

These provisions regarding changes with majority approval also apply to changes affecting any securities issued under a unit agreement, as the governing document.

In each case, the required approval must be given by written consent.

#### Unit Agreements will not be Qualified Under Trust Indenture Act
No unit agreement will be qualified as an indenture, and no unit agent will be required to qualify as a trustee, under the Trust Indenture Act. Therefore, holders of units issued under unit agreements will not have the protections of the Trust Indenture Act with respect to their units.

#### Mergers and Similar Transactions Permitted; No Restrictive Covenants or Events of Default
The unit agreements will not restrict our ability to merge or consolidate with, or sell our assets to, another corporation or other entity or to engage in any other transactions. If at any time we merge or consolidate with, or sell our assets substantially as an entirety to, another corporation or other entity, the successor entity will succeed to and assume our obligations under the unit agreements. We will then be relieved of any further obligation under these agreements.

The unit agreements will not include any restrictions on our ability to put liens on our assets, nor will they restrict our ability to sell our assets. The unit agreements also will not provide for any events of default or remedies upon the occurrence of any events of default.

#### Governing Law
The unit agreements and the units will be governed by Delaware law.

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#### Form, Exchange and Transfer
We will issue each unit in global—i.e., book-entry—form only. Units in book-entry form will be represented by a global security registered in the name of a depositary, which will be the holder of all the units represented by the global security. Those who own beneficial interests in a unit will do so through participants in the depositary's system, and the rights of these indirect owners will be governed solely by the applicable procedures of the depositary and its participants. We will describe book-entry securities, and other terms regarding the issuance and registration of the units in the applicable prospectus supplement.

Each unit and all securities comprising the unit will be issued in the same form.

If we issue any units in registered, non-global form, the following will apply to them. The units will be issued in the denominations stated in the applicable prospectus supplement. Holders may exchange their units for units of smaller denominations or combined into fewer units of larger denominations, as long as the total amount is not changed.

● holders may exchange or transfer their units at the office of the unit agent. Holders may also replace lost, stolen, destroyed or mutilated units at that office. We may appoint another entity to perform these functions or perform them ourselves.

● holders will not be required to pay a service charge to transfer or exchange their units, but they may be required to pay for any tax or other governmental charge associated with the transfer or exchange. The transfer or exchange, and any replacement, will be made only if our transfer agent is satisfied with the holder ' s proof of legal ownership. The transfer agent may also require an indemnity before replacing any units.

● if we have the right to redeem, accelerate or settle any units before their maturity, and we exercise our right as to less than all those units or other securities, we may block the exchange or transfer of those units during the period beginning 15 days before the day we mail the notice of exercise and ending on the day of that mailing, in order to freeze the list of holders to prepare the mailing. We may also refuse to register transfers of or exchange any unit selected for early settlement, except that we will continue to permit transfers and exchanges of the unsettled portion of any unit being partially settled. We may also block the transfer or exchange of any unit in this manner if the unit includes securities that are or may be selected for early settlement.

Only the depositary will be entitled to transfer or exchange a unit in global form, since it will be the sole holder of the unit.

#### Payments and Notices
In making payments and giving notices with respect to our units, we will follow the procedures as described in the applicable prospectus supplement.

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#### PLAN OF DISTRIBUTION
We may sell securities:

● through underwriters;

● through dealers;

● through agents;

● directly to purchasers; or

● through a combination of any of these methods or any other method permitted by law.

In addition, we may issue the securities as a dividend or distribution or in a subscription rights offering to our existing security holders.

We may directly solicit offers to purchase securities, or we may designate agents to solicit these offers. In the prospectus supplement relating to such an offering, we will name any agent that could be viewed as an underwriter under the Securities Act and describe any commissions that we must pay to any such agent. Any such agent will be acting on a best efforts basis for the period of its appointment or, if indicated in the applicable prospectus supplement, on a firm commitment basis. This prospectus may be used in connection with any offering of our securities through any of these methods or other methods described in the applicable prospectus supplement.

The distribution of the securities may be effected from time to time in one or more transactions:

● at a fixed price, or prices, which may be changed from time to time;

● at market prices prevailing at the time of sale;

● at prices related to such prevailing market prices; or

● at negotiated prices.

Each prospectus supplement will describe the method of distribution of the securities and any applicable restrictions.

The prospectus supplement with respect to the securities of a particular series will describe the terms of the offering of the securities, including the following:

● the name of the agent or any underwriters;

● the public offering or purchase price;

● any discounts and commissions to be allowed or paid to the agent or underwriters;

● all other items constituting underwriting compensation;

● any discounts and commissions to be allowed or paid to dealers; and

● any exchanges on which the securities will be listed.

If any underwriters or agents are used in the sale of the securities in respect of which this prospectus is delivered, we will enter into an underwriting agreement, equity distribution agreement or other agreement with them at the time of sale to them, and we will set forth in the prospectus supplement relating to such offering the names of the underwriters or agents and the terms of the related agreement with them.

In connection with the offering of securities, we may grant to the underwriters an option to purchase additional securities with an additional underwriting commission, as may be set forth in the accompanying prospectus supplement. If we grant any such option, the terms of such option will be set forth in the prospectus supplement for such securities.

If a dealer is used in the sale of the securities in respect of which the prospectus is delivered, we will sell such securities to the dealer, as principal. The dealer, who may be deemed to be an "underwriter" as that term is defined in the Securities Act, may then resell such securities to the public at varying prices to be determined by such dealer at the time of resale.

If we offer securities in a subscription rights offering to our existing security holders, we may enter into a standby underwriting agreement with dealers, acting as standby underwriters. We may pay the standby underwriters a commitment fee for the securities they commit to purchase on a standby basis. If we do not enter into a standby

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underwriting arrangement, we may retain a dealer-manager to manage a subscription rights offering for us. Agents, underwriters, dealers and other persons may be entitled under agreements which they may enter into with us to indemnification by us against certain civil liabilities, including liabilities under the Securities Act, and may be customers of, engage in transactions with or perform services for us in the ordinary course of business.

If so indicated in the applicable prospectus supplement, we will authorize underwriters or other persons acting as our agents to solicit offers by certain institutions to purchase securities from us pursuant to delayed delivery contracts providing for payment and delivery on the date stated in the prospectus supplement. Each contract will be for an amount not less than, and the aggregate amount of securities sold pursuant to such contracts shall not be less nor more than, the respective amounts stated in the prospectus supplement. Institutions with whom the contracts, when authorized, may be made include commercial and savings banks, insurance companies, pension funds, investment companies, educational and charitable institutions and other institutions, but shall in all cases be subject to our approval. Delayed delivery contracts will not be subject to any conditions except that:

● the purchase by an institution of the securities covered under that contract shall not at the time of delivery be prohibited under the laws of the jurisdiction to which that institution is subject; and

● if the securities are also being sold to underwriters acting as principals for their own account, the underwriters shall have purchased such securities not sold for delayed delivery. The underwriters and other persons acting as our agents will not have any responsibility in respect of the validity or performance of delayed delivery contracts.

Offered securities may also be offered and sold, if so indicated in the prospectus supplement, in connection with a remarketing upon their purchase, in accordance with a redemption or repayment pursuant to their terms, or otherwise, by one or more remarketing firms, acting as principals for their own accounts or as agents for us. Any remarketing firm will be identified and the terms of its agreement, if any, with us and its compensation will be described in the applicable prospectus supplement. Remarketing firms may be deemed to be underwriters in connection with their remarketing of offered securities.

Certain agents, underwriters and dealers, and their associates and affiliates, may be customers of, have borrowing relationships with, engage in other transactions with, or perform services, including investment banking services, for us or one or more of our respective affiliates in the ordinary course of business.

In order to facilitate the offering of the securities, any underwriters may engage in transactions that stabilize, maintain or otherwise affect the price of the securities or any other securities the prices of which may be used to determine payments on such securities. Specifically, any underwriters may over-allot in connection with the offering, creating a short position for their own accounts. In addition, to cover overallotments or to stabilize the price of the securities or of any such other securities, the underwriters may bid for, and purchase, the securities or any such other securities in the open market. Finally, in any offering of the securities through a syndicate of underwriters, the underwriting syndicate may reclaim selling concessions allowed to an underwriter or a dealer for distributing the securities in the offering if the syndicate repurchases previously distributed securities in transactions to cover syndicate short positions, in stabilization transactions or otherwise. Any of these activities may stabilize or maintain the market price of the securities above independent market levels. Any such underwriters are not required to engage in these activities and may end any of these activities at any time.

We may engage in at the market offerings into an existing trading market in accordance with Rule 415(a)(4) under the Securities Act. In addition, we may enter into derivative transactions with third parties, or sell securities not covered by this prospectus to third parties in privately negotiated transactions. If the applicable prospectus supplement so indicates, in connection with those derivatives, the third parties may sell securities covered by this prospectus and the applicable prospectus supplement, including in short sale transactions. If so, the third party may use securities pledged by us or borrowed from us or others to settle those sales or to close out any related open borrowings of stock, and may use securities received from us in settlement of those derivatives to close out any related open borrowings of stock. The third party in such sale transactions will be an underwriter and, if not identified in this prospectus, will be named in the applicable prospectus supplement (or a post-effective amendment). In addition, we may otherwise loan or pledge securities to a financial institution or other third party that in turn may sell the securities short using this prospectus and

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an applicable prospectus supplement. Such financial institution or other third party may transfer its economic short position to investors in our securities or in connection with a concurrent offering of other securities.

Under Rule 15c6-1 of the Exchange Act, trades in the secondary market generally are required to settle in one business day, unless the parties to any such trade expressly agree otherwise. The applicable prospectus supplement may provide that the original issue date for your securities may be more than one scheduled business day after the trade date for your securities. Accordingly, in such a case, if you wish to trade securities on any date prior to the first business day before the original issue date for your securities, you will be required, by virtue of the fact that your securities initially are expected to settle in more than one scheduled business day after the trade date for your securities, to make alternative settlement arrangements to prevent a failed settlement. The securities may be new issues of securities and may have no established trading market. The securities may or may not be listed on a national securities exchange. We can make no assurance as to the liquidity of or the existence of trading markets for any of the securities.

The specific terms of any lock-up provisions in respect of any given offering will be described in the applicable prospectus supplement.

The underwriters, dealers and agents may engage in transactions with us, or perform services for us, in the ordinary course of business for which they receive compensation.

The anticipated date of delivery of offered securities will be set forth in the applicable prospectus supplement relating to each offer.

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#### LEGAL MATTERS
Certain legal matters in connection with this offering will be passed upon for us by Goodwin Procter LLP, Boston, Massachusetts. Any underwriters will also be advised about the validity of the securities and other legal matters by their own counsel, which will be named in the prospectus supplement.

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#### EXPERTS
The consolidated financial statements of Altimmune, Inc. appearing in Altimmune, Inc.'s Annual Report (Form 10-K) for the year ended December 31, 2024 have been audited by Ernst & Young LLP, independent registered public accounting firm, as set forth in their report thereon, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing.

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#### WHERE YOU CAN FIND MORE INFORMATION
This prospectus is part of a registration statement we filed with the SEC. This prospectus does not contain all of the information set forth in the registration statement and the exhibits to the registration statement. For further information with respect to us and the securities we are offering under this prospectus, we refer you to the registration statement and the exhibits and schedules filed as a part of the registration statement. You should rely only on the information contained in this prospectus or incorporated by reference. We have not authorized anyone else to provide you with different information. We are not making an offer of these securities in any state where the offer is not permitted. You should not assume that the information in this prospectus is accurate as of any date other than the date on the front page of this prospectus, regardless of the time of delivery of this prospectus or any sale of the securities offered by this prospectus.

We file annual, quarterly and current reports, proxy statements, and other information with the SEC. The SEC maintains a web site at http://www.sec.gov that contains reports, proxy statements and other information about issuers, such as us, who file electronically with the SEC. The address of the SEC website is www.sec.gov.

We maintain a website at http://www.altimmune.com. The information contained on, or accessible through, our website is not incorporated by reference into this prospectus and, therefore, is not part of this prospectus or part of the accompanying prospectus supplement.

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#### INCORPORATION BY REFERENCE
The SEC allows us to incorporate by reference much of the information we file with the SEC, which means that we can disclose important information to you by referring you to those publicly available documents. The information that we incorporate by reference in this prospectus is considered to be part of this prospectus.

Because we are incorporating by reference future filings with the SEC, this prospectus is continually updated, and those future filings may modify or supersede some of the information included or incorporated in this prospectus. This means that you must look at all of the SEC filings that we incorporate by reference to determine if any of the statements in this prospectus or in any document previously incorporated by reference have been modified or superseded. This prospectus incorporates by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (in each case, other than those documents or the portions of those documents not deemed to be filed) between the date of the initial registration statement and the effectiveness of the registration statement and following the effectiveness of the registration statement until the offering of the securities under the registration statement is terminated or completed:

● our Annual Report on Form 10-K for the fiscal year ended December 31, 2024, filed with the SEC on February 27, 2025 (the " [2024 10-K](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000015/alt-20241231x10k.htm) ");

● our Quarterly Reports on Form 10-Q for the quarterly period ended [March 31, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000034/alt-20250331x10q.htm) , filed with the SEC on May 13, 2025; for the quarter ended [June 30, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000040/alt-20250630x10q.htm) , filed with the SEC on August 12, 2025 and for the quarter ended [September 30, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000064/alt-20250930x10q.htm) , filed with the SEC on November 6, 2025;

● our Current Reports on Form 8-K, as filed with the SEC on [February 25, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000003/alt-20250224x8k.htm) and [February 27, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000011/alt-20250224x8k.htm) , [May 13, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000031/alt-20250513x8k.htm) , [September 25, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000050/alt-20250925x8k.htm) , [October 3, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000053/alt-20251001x8k.htm) , [November 6, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000055/alt-20251106x8k.htm) and [November 6, 2025](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000067/alt-20251106x8k.htm) ; and

● the description of our common stock set forth in the registration statement on Form 8-A registering our common stock under Section 12 of the Exchange Act, which was filed as [Exhibit 4.1](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000015/alt-20241231xex4d1.htm) to our 2024 10-K, including any amendments or reports filed for purposes of updating such description.

We also incorporate by reference into this prospectus all documents (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items) that are filed by us with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (i) after the date of the initial filing of the registration statement of which this prospectus forms a part and prior to effectiveness of the registration statement, and (ii) after the date of this prospectus but prior to the termination of the offering. These documents include, without limitation, Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, as well as proxy statements. We will provide to each person, including any beneficial owner, to whom a prospectus is delivered, a copy of any or all of the information that has been incorporated by reference in the prospectus but not delivered with the prospectus.

You may request a copy of these filings, at no cost, by contacting us, either orally or in writing, at the following:

Altimmune, Inc.

910 Clopper Road, Suite 201S

Gaithersburg, Maryland

Attention: Chief Financial Officer

(240) 654-1450

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![Graphic](alt-20251113xs3a007.jpg)

**$400,000,000**

**Common Stock**

**Preferred Stock**

**Debt Securities**

**Warrants**

**Units**

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#### PROSPECTUS

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**, 2025**

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We have not authorized any dealer, salesperson or other person to give any information or represent anything not contained in this prospectus. You must not rely on any unauthorized information. If anyone provides you with different or inconsistent information, you should not rely on it. This prospectus does not offer to sell any securities in any jurisdiction where it is unlawful. Neither the delivery of this prospectus, nor any sale made hereunder, shall create any implication that the information in this prospectus is correct after the date hereof.

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**Part II—INFORMATION NOT REQUIRED IN PROSPECTUS**

**Item 14. Other Expenses of Expenses of Issuance and Distribution**

The following table sets forth the fees and expenses payable by us in connection with the sale of the offered securities being registered hereby, other than underwriting discounts and commissions. All amounts are estimates except the SEC registration fee.

---

| | |
|:---|:---|
| Securities and Exchange Commission registration fee | $55240 |
| Legal fees and expenses | \* |
| Accounting fees and expenses | \* |
| Printing fees and expenses | \* |
| Transfer agent and trustee fees | \* |
| Miscellaneous | \* |
| Total | $\* |

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\* These fees and expenses depend on the securities offered and the number of issuances and accordingly cannot be estimated at this time.

**Item 15. Indemnification of Directors and Officers**

Section 145 of the Delaware General Corporation Law, or the DGCL, authorizes a corporation to indemnify its directors and officers against liabilities arising out of actions, suits and proceedings to which they are made or threatened to be made a party by reason of the fact that they have served or are currently serving as a director or officer to a corporation. The indemnity may cover expenses (including attorneys' fees) judgments, fines and amounts paid in settlement actually and reasonably incurred by the director or officer in connection with any such action, suit or proceeding if the director or officer acted in good faith and in a manner the director or officer reasonably believed to be in or not opposed to the best interests of the corporation, and, with respect to any criminal action or proceeding, had no reasonable cause to believe the director or officer's conduct was unlawful. Section 145 permits corporations to pay expenses (including attorneys' fees) incurred by directors and officers in advance of the final disposition of such action, suit or proceeding upon receipt of an undertaking by or on behalf of such director or officer to repay such amount if it shall ultimately be determined that such director or officer is not entitled to be indemnified by the corporation as authorized in Section 145. In addition, Section 145 provides that a corporation has the power to purchase and maintain insurance on behalf of its directors and officers against any liability asserted against them and incurred by them in their capacity as a director or officer, or arising out of their status as such, whether or not the corporation would have the power to indemnify the director or officer against such liability under Section 145.

We have adopted provisions in both our certificate of incorporation and bylaws that limit or eliminate the personal liability of our directors to the fullest extent permitted by the DGCL, as it now exists or may in the future be amended. Consequently, a director is not personally liable to us or our stockholders for monetary damages or breach of fiduciary duty as a director, except for liability for:

● any breach of the directors duty of loyalty to us or our stockholders;

● any act or omission not in good faith or that involves intentional misconduct or a knowing violation of law;

● any unlawful payments related to dividends or unlawful stock purchases, redemptions or other distributions; or

● any transaction from which the director derived an improper personal benefit.

These limitations of liability do not alter director liability under the federal securities laws and do not affect the availability of equitable remedies such as an injunction or rescission.

In addition, our Bylaws, as amended, provide the Company with the power to:

● indemnify our officers, directors, employees and agents or any person serving at the Company's request as a director, officer, employee or agent of another corporation, partnership, joint venture, trust or other enterprise, to the fullest extent permitted by the DGCL, as it now exists or may in the future be amended; and

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● to advance reasonable expenses, including attorneys' fees, to our directors and, in the discretion of our board of directors, to our officers and certain employees, in connection with legal proceedings relating to their service for or on behalf of us, subject to limited exceptions.

We have entered into indemnification agreements with each of our directors and executive officers. These agreements provide that, in exchange for each person's continued service as a director, officer or other employee, as applicable, we will indemnify each of our directors, certain of our executive officers and, at times, their affiliates to the fullest extent permitted by Delaware law. We will advance expenses, including attorneys' fees (but excluding judgments, fines and settlement amounts), to each indemnified director, executive officer or affiliate in connection with any proceeding in which indemnification is available and we will indemnify our directors and officers for any action or proceeding arising out of that person's services as a director or officer brought on behalf of us or in furtherance of our rights. Additionally, certain of our directors or officers may have certain rights to indemnification, advancement of expenses or insurance provided by their affiliates or other third parties, which indemnification relates to and might apply to the same proceedings arising out of such director's or officer's services as a director referenced herein. Nonetheless, we have agreed in the indemnification agreements that our obligations to those same directors or officers are primary and any obligation of such affiliates or other third parties to advance expenses or to provide indemnification for the expenses or liabilities incurred by those directors are secondary.

The foregoing description of the Indemnification Agreements does not purport to be complete and is qualified in its entirety by reference to the actual agreement, a form of which is attached as an exhibit to the Company's Current Report on Form 8-K, filed on January 27, 2009.

We also maintain general liability insurance which covers certain liabilities of our directors and officers arising out of claims based on acts or omissions in their capacities as directors or officers, including liabilities under the Securities Act.

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#### Item 16. Exhibits and Financial Statement Schedules
(a)Exhibits

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| | | | | | |
|:---|:---|:---|:---|:---|:---|
| &nbsp;&nbsp;**Exhibit No.** | &nbsp;&nbsp;**Description** | &nbsp;&nbsp;**Form** | &nbsp;&nbsp;**File Number** | &nbsp;&nbsp;**Date of Filing** | &nbsp;&nbsp;**Exhibit Number** |
| &nbsp;&nbsp;1.1\*\* | &nbsp;&nbsp;Form of Underwriting Agreement |  |  |  |  |
| &nbsp;&nbsp;3.1 | &nbsp;&nbsp;[Amended and Restated Certificate of Incorporation, dated October 17, 2017](https://www.sec.gov/Archives/edgar/data/1326190/000119312517312751/d470504dex31.htm) | &nbsp;&nbsp;8-K | &nbsp;&nbsp;001-32587 | &nbsp;&nbsp;October 18, 2017 | &nbsp;&nbsp;3.1 |
| &nbsp;&nbsp;3.2 | &nbsp;&nbsp;[Certificate of Amendment to Amended and Restated Certificate of Incorporation](https://www.sec.gov/Archives/edgar/data/1326190/000119312518272896/d621454dex31.htm) | &nbsp;&nbsp;8-K | &nbsp;&nbsp;001-32587 | &nbsp;&nbsp;September 13, 2018 | &nbsp;&nbsp;3.1 |
| &nbsp;&nbsp;3.3 | &nbsp;&nbsp;[Certificate of Amendment to Amended and Restated Certificate of Incorporation](https://www.sec.gov/Archives/edgar/data/1326190/000119312518272896/d621454dex32.htm) | &nbsp;&nbsp;8-K | &nbsp;&nbsp;001-32587 | &nbsp;&nbsp;September 13, 2018 | &nbsp;&nbsp;3.2 |
| &nbsp;&nbsp;4.3 | &nbsp;&nbsp;[Form of Specimen Common Stock Certificate](https://www.sec.gov/Archives/edgar/data/1326190/000119380507002438/e602624_ex4-2.htm) | &nbsp;&nbsp;8-K/A | &nbsp;&nbsp;001-32587 | &nbsp;&nbsp;September 24, 2007 | &nbsp;&nbsp;4.2 |
| &nbsp;&nbsp;4.4 | &nbsp;&nbsp;[Form of Senior Indenture between Registrant and one or more trustees to be named](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000070/alt-20251106xex4d4.htm) | &nbsp;&nbsp;S-3 | &nbsp;&nbsp;333-291329 | &nbsp;&nbsp;November 6, 2025 | &nbsp;&nbsp;4.4 |
| &nbsp;&nbsp;4.5 | &nbsp;&nbsp;[Form of Subordinated Indenture between Registrant and one or more trustees to be named](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000070/alt-20251106xex4d5.htm) | &nbsp;&nbsp;S-3 | &nbsp;&nbsp;333-291329 | &nbsp;&nbsp;November 6, 2025 | &nbsp;&nbsp;4.5 |
| &nbsp;&nbsp;4.6\*\* | &nbsp;&nbsp;Form of Certificate of Designations |  |  |  |  |
| &nbsp;&nbsp;4.7\*\* | &nbsp;&nbsp;Form of Warrant Agreements |  |  |  |  |
| &nbsp;&nbsp;4.8\*\* | &nbsp;&nbsp;Form of Unit Agreement and Unit Certificate |  |  |  |  |
| &nbsp;&nbsp;4.9\*\* | &nbsp;&nbsp;Form of Preferred Stock Certificate |  |  |  |  |
| &nbsp;&nbsp;5.1 | &nbsp;&nbsp;[Opinion of Goodwin Procter LLP](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000070/alt-20251106xex5d1.htm) | &nbsp;&nbsp;S-3 | &nbsp;&nbsp;333-291329 | &nbsp;&nbsp;November 6, 2025 | &nbsp;&nbsp;5.1 |
| &nbsp;&nbsp;23.1\* | &nbsp;&nbsp;[Consent of Ernst & Young LLP, Independent Registered Public Accounting Firm](alt-20251113xex23d1.htm) |  |  |  |  |
| &nbsp;&nbsp;23.2 | &nbsp;&nbsp;[Consent of Goodwin Procter LLP (included in Exhibit 5.1)](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000070/alt-20251106xex5d1.htm) | &nbsp;&nbsp;S-3 | &nbsp;&nbsp;333-291329 | &nbsp;&nbsp;November 6, 2025 | &nbsp;&nbsp;23.2 |
| &nbsp;&nbsp;24.1 | &nbsp;&nbsp;[Power of Attorney (included on signature pages)](https://www.sec.gov/Archives/edgar/data/1326190/000132619025000070/alt-20251106xs3.htm#SIGNATURES_AND_POA) | &nbsp;&nbsp;S-3 | &nbsp;&nbsp;333-291329 | &nbsp;&nbsp;November 6, 2025 | &nbsp;&nbsp;24.1 |

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| | | | | | |
|:---|:---|:---|:---|:---|:---|
| &nbsp;&nbsp;25.1\*\*\* | &nbsp;&nbsp;Form T-1 Statement of Eligibility of Trustee for Senior Indenture under the Trust Indenture Act of 1939 |  |  |  |  |
| &nbsp;&nbsp;25.2\*\*\* | &nbsp;&nbsp;Form T-1 Statement of Eligibility of Trustee for Subordinated Indenture under the Trust Indenture Act of 1939 |  |  |  |  |
| &nbsp;&nbsp;107 | &nbsp;&nbsp;[Fee Table](https://www.sec.gov/ix?doc=/Archives/edgar/data/1326190/000132619025000070/alt-20251106xexfees.htm) | &nbsp;&nbsp;S-3 | &nbsp;&nbsp;333-291329 | &nbsp;&nbsp;November 6, 2025 | &nbsp;&nbsp;107 |

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\* Filed herewith.

\*\* To be filed, if necessary, by amendment or as an exhibit to a document to be incorporated or deemed to be incorporated by reference in this registration statement, including a Current Report on Form 8-K.

\*\*\* To be filed pursuant to Section 305(b)(2) of the Trust Indenture Act of 1939.

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**Item 17. Undertakings**

The undersigned registrant hereby undertakes:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;i. To include any prospectus required by Section 10(a)(3) of the Securities Act of 1933;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ii. To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;iii. To include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement; *provided, however*, that paragraphs (1)(i), (l)(ii) and (1)(iii) above do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the SEC by the registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934 that are incorporated by reference in the registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the registration statement;

*provided, however*, that paragraphs (1)(i), (1)(ii) and (1)(iii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the SEC by a registrant pursuant to Section 13 or Section 15(d) of the Exchange Act, that are incorporated by reference in this registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of this registration statement.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(4) That, for the purpose of determining liability under the Securities Act of 1933 to any purchaser:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;i. Each prospectus filed by the registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ii. Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5), or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(l)(i), (vii), or (x) for the purpose of providing the information required by Section 10(a) of the Securities Act of 1933 shall be deemed to be part of and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which that prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof; provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such effective date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(5) That, for the purpose of determining liability of the registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities, the undersigned registrant undertakes that in a primary offering of

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securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;i. Any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ii. Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;iii. The portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;iv. Any other communication that is an offer in the offering made by the undersigned registrant to the purchaser;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(6) That, for purposes of determining any liability under the Securities Act of 1933, each filing of the registrant's annual report pursuant to Section 13(a) or Section 15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan's annual report pursuant to Section 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(7) Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act of 1933 and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act of 1933 and will be governed by the final adjudication of such issue;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(8) To file an application for the purpose of determining the eligibility of the trustee to act under subsection (a) of Section 310 of the Trust Indenture Act of 1939 in accordance with the rules and regulations prescribed by the SEC under Section 305(b)(2) of the Trust Indenture Act of 1939.

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[**Table of Contents**](#TOC)

#### SIGNATURES
Pursuant to the requirements of the Securities Act of 1933, the registrant has duly caused this Amendment No. 1 to the Registration Statement on Form S-3 to be signed on its behalf by the undersigned, thereunto duly authorized, in Gaithersburg, Maryland, on the 13th day of November, 2025.

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| | |
|:---|:---|
| **ALTIMMUNE, INC.** | **ALTIMMUNE, INC.** |
| **By:** | **/s/ Vipin K. Garg** |
|  | **Vipin K. Garg** |
|  | **President and Chief Executive Officer** |

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Pursuant to the requirements of the Securities Act of 1933, this Amendment No. 1 to the Registration Statement on Form S-3 has been signed by the following persons in the capacities and on the dates indicated.

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| | | |
|:---|:---|:---|
| **Signature** | **Title** | **Date** |
| /s/ Vipin K. Garg | *President, Chief Executive Officer and*  | November 13, 2025 |
| Vipin K. Garg | *Director (Principal Executive Officer)* |  |
| /s/ Gregory Weaver | *Chief Financial Officer, (Principal*  | November 13, 2025 |
| Gregory Weaver | *Financial Officer and Principal Accounting Officer)* |  |
| \* | *Chairman of the Board* | November 13, 2025 |
| Jerome Durso |  |  |
| \* | *Director* | November 13, 2025 |
| John Gill |  |  |
| \* | *Director* | November 13, 2025 |
| Philip Hodges |  |  |
| \* | *Director* | November 13, 2025 |
| Diane Jorkasky, M.D. |  |  |
| \* | *Director* | November 13, 2025 |
| Teri Lawver |  |  |
| \* | *Director* | November 13, 2025 |
| Wayne Pisano |  |  |
| \* | *Director* | November 13, 2025 |
| Mitchel Sayare, Ph.D. |  |  |
| \* | *Director* | November 13, 2025 |
| Klaus O. Schafer, M.D. |  |  |
| \* | *Director* | November 13, 2025 |
| Catherine Sohn, Pharm D |  |  |

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| | |
|:---|:---|
| \*By: | /s/ Vipin K. Garg |
|  | Name: Vipin K. Garg |
|  | Title: Attorney-in-fact |

---

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## Exhibit 23.1

**Exhibit 23.1**

**Consent of Independent Registered Public Accounting Firm**

We consent to the reference to our firm under the caption "Experts" in Amendment No. 1 to the Registration Statement (Form S-3 No. 333-291329) and related Prospectus of Altimmune, Inc. dated November 13, 2025 for the registration of up to $400,000,000 of its common stock, preferred stock, debt securities, warrants or units and to the incorporation by reference therein of our report dated February 27, 2025, with respect to the consolidated financial statements of Altimmune, Inc. included in its Annual Report (Form 10-K) for the year ended December 31, 2024, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP

Iselin, New Jersey

November 13, 2025

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