Document:

EX-10.5

 Exhibit 10.5 

ICOSAVAX, INC. 

August 15, 2019 
 Tadataka Yamada 

Re:    Icosavax, Inc. Board of Directors 

Dear Tachi, 
 In
connection with the transactions contemplated by the Series A Preferred Stock Purchase Agreement, dated as of August 15, 2019, by and among the Company and the Purchasers named therein (the “Transaction”), we are
amending and restating the terms of your position on the Board of Directors (the “Board”) of Icosavax, Inc. (the “Company”) as Chairman of the Board, as previously set forth on that certain offer
letter, by and between you and the Company, dated January 1, 2018 (the “Prior Letter”). Please note that this amended and restated offer letter (this “Letter”) is contingent on the closing of the
Transaction (the “Closing”), and shall become effective as of the Closing (the “Effective Date”). In the event the Closing does not occur on or before December 31, 2019, this Letter shall have no
force and effect and shall be null and void, and the Prior Letter shall remain in effect. 
 In your capacity as Chairman of
the Board, you will continue to perform advisory duties customarily associated with the position, participate in regularly scheduled and special Board meetings, participate in conference calls of the Board, meet or otherwise periodically confer with
Board members, committees of the Board and Company executives, and provide assistance to the Company’s executive team with occasional meetings, site visits, conference calls and advice on an as-needed
basis (the “Services”). 
 Following the Effective Date, you will paid an annual cash fee of
$100,000, paid quarterly, for your services as Chairman. Moreover, as a member of the Board, the Company will reimburse you for reasonable travel and other expenses to attend Board meetings and other Board-related functions (such as site visits).

 Upon the Effective Date, you shall be eligible to receive a one-time bonus equal
to (a) (i) $100,000, divided by (ii) 365, multiplied by (b) the number of days elapsed from January 1, 2018 through and including the Effective Date, which bonus shall be paid within ten (10) days following the Effective Date, subject
to applicable payroll deductions and withholdings. 
 You will continue to serve as the Chairman of the Board until the
earlier of your resignation, removal from the Board or death, or your successor as Chairman of the Board is duly appointed by the Board. You may be removed from the Board at any time in accordance with terms of the Company’s Bylaws. You will
not be an employee or agent of the Company. You will not be eligible for any employee benefits. Any taxes shall be solely your responsibility. 

In your capacity as a director of the Company, you will be expected not to use or disclose any confidential information,
including, but not limited to, trade secrets of any current or former employer or other person or entity to whom you have an obligation of confidentiality. Rather, you will be expected to use only information that is generally known and used by
persons with training and experience comparable to your own, that is common knowledge in the industry or otherwise legally in the public domain, or that is otherwise provided by the Company. You acknowledge that as a result of the Services, you will
obtain confidential information and proprietary information relating to or provided by the Company and its affiliates. During and after your service with the Company, you shall not use for your benefit or disclose confidential information,
proprietary information, knowledge or data relating to or provided by the Company and its affiliates; provided, however, that, except as provided under applicable law, this obligation shall not apply to information that (a) was publicly known
and available in the public domain at the time of disclosure, or later becomes publicly known and available in the public domain other than through your 

 
failure to keep such information confidential, (b) was in your possession at the time of disclosure or is provided to you by a third party, in each case without duty of confidentiality,
(c) was independently developed by you without incorporating or using Company information or resources, as demonstrated by records contemporaneously maintained, or (d) is disclosed with the express consent of the Company. Any proprietary
inventions or other intellectual property rights that you may develop (including, but not limited to, patents, copyrights, trademarks, trade secrets, technology, contract and licensing rights, business plans or other proprietary rights), either
alone or jointly with others, during the course of performing the Services for the Company is assigned by you to the Company and you agree to execute, when requested, such additional documentation deemed necessary by the Company to assign all
rights, title and interest to such inventions or property. You also represent and warrant that you have the full right and power to enter into and perform this letter agreement and there is no other existing contract or duty on your part
inconsistent with the terms of this letter agreement (including, but not limited to, any conflict of interest policy). Additionally, as a reminder, as a member of the Board, you will have fiduciary duties to the Company and its members. 

Notwithstanding the foregoing, pursuant to 18 U.S.C. Section 1833(b), you shall not be held criminally or civilly liable
under any Federal or State trade secret law for the disclosure of a trade secret that: (a) is made in confidence to a Federal, State, or local government official, either directly or indirectly, or to an attorney, and solely for the purpose of
reporting or investigating a suspected violation of law; or (b) is made in a complaint or other document filed in a lawsuit or other proceeding, if such filing is made under seal. 

To avoid conflicts of interest, it is expected that directors will disclose any personal interest they may have in a
transaction that the Board considers or in which the Company otherwise is a party. Directors shall recuse themselves from participation in any decision in which there is a conflict between their personal interests and the interests of the Company.
Any such “related party transaction” involving a director must be reviewed and approved by the Board (or a committee designated by the Board). 

This Letter constitutes the entire agreement between you and the Company. This Letter supersedes any other agreements or
promises made to you by anyone, whether oral or written, including, without limitation, the Prior Letter, and it may only be modified in a writing signed by a duly authorized officer of the Company. This Letter shall be construed and enforced in
accordance with the laws of the State of Washington without regard to conflicts of law principles. We look forward to your favorable reply and to continue a productive relationship. 

 Sincerely, 

ICOSAVAX, INC. 
  

			
	 By:
	 	 /s/ Adam K. Simpson

		 	  Adam K. Simpson, Chief Executive Officer

 ACKNOWLEDGED AND AGREED: 

 

	
	 /s/ Tadataka Yamada

	 Tadataka YamadaEX-10.6

 Exhibit 10.6 

ICOSAVAX, INC. 

May 11, 2020 
 Adam Simpson 

Re:    Employment Letter Agreement 

Dear Adam: 

This amended and restated employment letter agreement (this “Agreement”) amends and restates that
certain employment letter agreement, dated August 15, 2019 (the “Prior Agreement”), by and between the Company and you (also referred herein as “Employee” and together, the
“Parties”). This Agreement sets forth the terms of your continued employment with Icosavax, Inc. (the “Company”), effective as of February 21, 2020. In consideration of the mutual promises herein
contained, the Parties agree as follows: 
 1.    Position. Employee will continue to serve in
the position of Chief Executive Officer. Employee will continue to report to the Company’s Board of Directors (the “Board”), and shall be responsible for the duties customarily associated with this position and such
other duties assigned by the Company. Employee will work remotely. Employee will be employed on a part-time basis and will spend seventy-five percent (75%) of Employee’s business time and efforts towards the performance of his duties for the
Company. Employee will also serve as a member of the Board. 
 2.    Base Salary and Employee
Benefits. 
 (a)    Salary. Employee’s base salary will be $375,000.00 per year (the
“Base Salary”), less payroll deductions and withholdings, paid on the Company’s normal payroll schedule. 

(b)    Benefits. During his employment, Employee will be eligible to participate in the standard
benefits plans offered to similarly situated employees by the Company from time to time, subject to plan terms and generally applicable Company policies. A full description of these benefits will be available upon request. Employee will be eligible
to accrue vacation or paid time off in accordance with the Company’s policies as in effect from time to time. The Company may change compensation and benefits from time to time in its discretion. 

(c)    Expenses. All reasonable business expenses that are documented by Employee and incurred in
the ordinary course of business will be reimbursed in accordance with the Company’s standard policies and procedures. 

3.    Annual Bonus. Employee will be eligible to earn an annual performance bonus of up to
forty-five percent (45%) of Employee’s Base Salary rate (the “Annual Bonus”) for performance at “targeted” levels. The Annual Bonus will be based upon an assessment by the Board of Employee’s performance
and the Company’s attainment of written targeted goals as set by the Board in its sole discretion. Bonus payments, if any, will be subject to applicable payroll deductions and withholdings. Following the close of each calendar year, the Board
will determine whether Employee has earned an Annual Bonus, and the amount of any such bonus, based on the achievement of such goals. No amount of Annual Bonus is guaranteed, and Employee must be an employee on the Annual Bonus payment date to be
eligible to receive an Annual Bonus; except as provided in Section 5 below, no partial or prorated 

 
bonuses will be provided. The Annual Bonus, if earned, will be paid no later than March 15 of the calendar year after the applicable bonus year. 

4.    At-Will Employment Relationship. Employee may
terminate his employment with the Company at any time and for any reason whatsoever simply by notifying the Company. Likewise, the Company may terminate Employee’s employment at any time, with or without cause or advance notice. Employee’s
employment at-will status can only be modified in a written agreement signed by Employee and by an officer of the Company. 

5.    Severance Benefits. If, at any time, the Company terminates Employee’s employment
without Cause or Employee resigns for Good Reason (either such termination referred to as a “Qualifying Termination”), provided such termination or resignation also constitutes a Separation from Service (as defined below),
then subject to Sections 7 and 8 below, Employee’s continued compliance with the terms of this Agreement (including without limitation Section 10 below) and Employee’s resignation from any and all positions Employee may hold with the
Company, to be effective no later than Employee’s Separation from Service date (or such other date requested or permitted by the Board), the Company will provide Employee with the following severance benefits (the “Severance
Benefits”): 
 (a)    Cash Severance. Upon a Qualifying Termination, the Company
will pay Employee, as cash severance (i) twelve (12) months of Employee’s Base Salary in effect as of Employee’s Separation from Service date, less applicable payroll deductions and withholdings (the “Base
Severance”), plus (ii) in the event of a Qualifying Termination that occurs within eighteen (18) months following the closing of a Change in Control, an amount equal to Employee’s “target” Annual Bonus for the
year in which Employee’s Qualifying Termination occurs (the “Bonus Severance,” and with the “Base Severance,” the “Severance”). 

Except in the case of a Qualifying Termination that occurs within eighteen (18) months following the closing of a Change
in Control, the Base Severance will be paid in installments in the form of continuation of Employee’s Base Salary payments, paid on the Company’s ordinary payroll dates, commencing on the Company’s first regular payroll date that is
more than sixty (60) days following Employee’s Separation from Service date. The first such installment shall be for any accrued Base Salary for the sixty (60)-day period plus the period from the
sixtieth (60th) day until the regular payroll date, if applicable. All salary continuation payments thereafter, if any, shall be made on the Company’s regular payroll dates. 

In the case of a Qualifying Termination that occurs within eighteen (18) months following the closing of a Change in
Control, the Base Severance will be paid in a lump sum on the Company’s first regular payroll date that is more than sixty (60) days following Employee’s Separation from Service date. 

Any Bonus Severance will be paid in a lump sum on the Company’s first regular payroll date that is more than sixty
(60) days following Employee’s Separation from Service date, but in any event no later than March 15 of the year following the year in which Employee’s Separation from Service date occurs. 

(b)    COBRA Severance. As additional severance, in the event of Employee’s Qualifying
Termination, the Company will continue to pay the cost of Employee’s health care coverage in effect at the time of Employee’s Separation from Service for twelve (12) months (the “COBRA Coverage Period”), either
under the Company’s regular health plan (if permitted) or by paying Employee’s COBRA premiums (the “COBRA Severance”). The Company’s obligation to pay the COBRA Severance on Employee’s behalf will cease if
Employee obtains health care coverage from another source (e.g., a new 

 
employer or spouse’s benefit plan), unless otherwise prohibited by applicable law. Employee must notify the Company within two (2) weeks if Employee obtains coverage from a new source.
This payment of COBRA Severance by the Company would not expand or extend the maximum period of COBRA coverage to which Employee would otherwise be entitled under applicable law. Notwithstanding the above, if the Company determines in its sole
discretion that it cannot provide the foregoing COBRA Severance without potentially violating applicable law (including, without limitation, Section 2716 of the Public Health Service Act), or if the Company otherwise elects, in its sole
discretion, the Company shall in lieu thereof provide to Employee a taxable monthly payment in an amount equal to the monthly COBRA premium that Employee would be required to pay to continue Employee’s group health coverage in effect on the
date of Employee’s termination (which amount shall be based on the premium for the first month of COBRA coverage), which payments shall be made on the last day of each month regardless of whether Employee elects COBRA continuation coverage and
shall end on the earlier of (x) the date upon which Employee obtains other coverage or (y) the last day of applicable COBRA Coverage Period. 

(c)    Accelerated Vesting. 

(i)    In the event of Employee’s Qualifying Termination, then (A) with respect to
Employee’s then-unvested Stock Awards granted prior to the date of the closing of the transactions contemplated by the Series A Preferred Stock Purchase Agreement, dated as of August 15, 2019, by and among the Company and the Purchasers
named therein (the “Transaction Closing Date” and such awards, the “Existing Stock Awards”), all such Existing Stock Awards shall be deemed vested effective immediately prior to such termination, and
(B) with respect to Employee’s then-unvested Stock Awards granted on or after the Transaction Closing Date (the “New Stock Awards”), provided such termination or resignation also constitutes a Separation from
Service, then such number of Employee’s New Stock Awards shall be deemed vested effective immediately prior to such termination as would have vested by their terms during the twelve (12) months following Employee’s date of termination
had Employee remained in the service of or employed by the Company during such period; provided that (x) Employee complies with Sections 7 and 8 below, (y) Employee continues to comply with the terms of this Agreement (including without
limitation Section 10 below) and (z) Employee resigns from any and all positions Employee holds with the Company, with such resignations to be effective no later than Employee’s Separation from Service date (or such other date
requested or permitted by the Board); provided, however, that Employee’s services shall not be considered to have been terminated without Cause or for Good Reason if Employee ceases to serve as Chief Executive Officer but continues to serve as
a member of the Board, in which case the foregoing acceleration shall then be triggered upon a termination of Employee’s service as a member of the Board without Cause or for Good Reason. 

(ii)    In the event of a Change in Control, then 50% of Employee’s then-unvested Existing Stock
Awards shall be deemed vested effective immediately prior to such Change in Control. 
 (iii)    In the
event of Employee’s termination of employment due to death or disability, then all Employee’s then-unvested Existing Stock Awards shall be deemed vested effective immediately prior to such termination. 

The foregoing accelerated vesting provisions are hereby referred to as the “Accelerated Vesting” and are deemed to be a part of each
Stock Award and to amend and supersede any provision in any agreement or plan regarding such Stock Award, even if such Accelerated Vesting provisions are less favorable. In the event of any conflict between the foregoing Accelerated Vesting
provisions and the terms of any Stock Award, including any Existing Stock Award, the Accelerated Vesting provisions shall apply. Notwithstanding the foregoing, the Accelerated Vesting shall be in addition to, and not in any way in limitation of, the
accelerated vesting provisions set forth in that certain Restricted Stock Purchase 

 
Agreement dated as of December 11, 2017, between the Company and The Adam K. and Maria M. Simpson Family Trust DTD 04/27/07, as amended from time to time, pursuant to which the Founders
Shares were issued to Employee. Notwithstanding the foregoing, any Stock Award granted after the Transaction Closing Date may be subject to additional accelerated vesting provisions in connection with a Change in Control, pursuant to the terms and
conditions set forth in such Stock Award’s applicable award agreement. 
 6.    Resignation
Without Good Reason; Termination for Cause; Death or Disability. If, at any time, Employee resigns his employment with the Company without Good Reason, or the Company terminates Employee’s employment for Cause, or Employee’s employment
with the Company terminates for any reason not entitling Employee to the Severance Benefits or Accelerated Vesting pursuant to Section 5 above, including (other than with respect to the Accelerated Vesting) as a result of Employee’s death
or disability, then Employee will receive his Base Salary accrued through his last day of employment. Under these circumstances, Employee will not be entitled to any other form of compensation from the Company, including any Severance Benefits or
Accelerated Vesting, other than Employee’s rights to the vested portion of Employee’s Stock Awards and any other rights to which Employee is entitled under the Company’s benefit programs. In addition, Employee shall resign from any
and all positions Employee holds with the Company, with such resignations to be effective no later than the date of Employee’s employment termination (or such other date requested or permitted by the Board). 

7.    Conditions to Receipt of Severance Benefits and Accelerated Vesting. Prior to and as a
condition to Employee’s, or Employee’s estate or legal representative, as applicable, receipt of the Severance Benefits or Accelerated Vesting described above, Employee, or Employee’s estate or legal representative, as applicable,
shall timely execute and deliver to the Company a release of claims in favor of and in a form acceptable to the Company (the “Release”) and allow the Release to become effective according to its terms (by not invoking any
legal right to revoke it) within sixty (60) days following Employee’s Separation from Service date. 

8.    Compliance with Section 409A. It is intended that the Severance Benefits
and Accelerated Vesting set forth in this Agreement satisfy, to the greatest extent possible, the exemptions from the application of Section 409A of the Code (Section 409A, together with any state law of similar effect,
“Section 409A”) provided under Treasury Regulations 1.409A-1(b)(4), 1.409A-1(b)(5) and 1.409A-1(b)(9). For purposes of Section 409A (including, without limitation, for purposes of Treasury Regulations 1.409A-2(b)(2)(iii)), Employee’s right to receive
any installment payments under this Agreement (whether severance payments, reimbursements or otherwise) shall be treated as a right to receive a series of separate payments and, accordingly, each installment payment hereunder shall at all times be
considered a separate and distinct payment. Notwithstanding any provision to the contrary in this Agreement, if the Company (or, if applicable, the successor entity thereto) determines that the Severance Benefits or Accelerated Vesting constitute
“deferred compensation” under Section 409A and Employee is, on the date of Employee’s Separation from Service, a “specified employee” of the Company or any successor entity thereto, as such term is defined in
Section 409A(a)(2)(B)(i) of the Code, then, solely to the extent necessary to avoid the incurrence of adverse personal tax consequences under Section 409A, the timing of the Severance Benefits and Accelerated Vesting shall be delayed until
the earliest of: (a) the date that is six (6) months and one (1) day after Employee’s Separation from Service date, (b) the date of Employee’s death, or (c) such earlier date as permitted under Section 409A
without the imposition of adverse taxation. Upon the first business day following the expiration of such applicable Code Section 409A(a)(2)(B)(i) period, all payments or benefits deferred pursuant to this Section 8 shall be paid in a lump
sum or provided in full by the Company (or the successor entity thereto, as applicable), and any remaining payments due shall be paid as otherwise provided herein. No interest shall be due on any amounts so deferred. The Severance Benefits and
Accelerated Vesting are intended to qualify for an exemption from application of Section 409A or comply with its requirements to the extent necessary to 

 
avoid adverse personal tax consequences under Section 409A, and any ambiguities herein shall be interpreted accordingly. Any reimbursement of expenses or
in-kind benefits payable under this Agreement shall be made in accordance with Treasury Regulation Section 1.409A-3(i)(1)(iv) and shall be paid on or before the
last day of Employee’s taxable year following the taxable year in which Employee incurred the expenses. The amount of expenses reimbursed or in-kind benefits payable in one year shall not affect the
amount eligible for reimbursement or in-kind benefits payable in any other taxable year of Employee, and Employee’s right to reimbursement for such amounts shall not be subject to liquidation or exchange
for any other benefit. 
 9.    Withholding Taxes. All forms of compensation referred to in this
Agreement will be subject to reduction to reflect applicable withholding and payroll taxes. 

10.    Compliance with Confidential Information and Inventions Agreement and Company Policies. In
the performance of services for the Company, Employee will be expected to abide by Company rules and policies. Employee and the Company have entered into a Confidential Information and Inventions Assignment Agreement attached hereto as Exhibit
A which prohibits unauthorized use or disclosure of the Company’s proprietary information, among other obligations. Employee agrees to perform each and every obligation of Employee therein contained. Any references in your Confidential
Information and Inventions Assignment Agreement to the Prior Agreement shall be deemed to be amended to refer to this Agreement. Notwithstanding the foregoing or in the Confidential Information and Inventions Assignment Agreement, pursuant to
18 U.S.C. Section 1833(b), Employee shall not be held criminally or civilly liable under any Federal or State trade secret law for the disclosure of a trade secret that: (a) is made in confidence to a Federal, State, or local government
official, either directly or indirectly, or to an attorney, and solely for the purpose of reporting or investigating a suspected violation of law; or (b) is made in a complaint or other document filed in a lawsuit or other proceeding, if such
filing is made under seal. 
 11.    Protection of Third Party Information. In Employee’s
work for the Company, Employee will be expected not to use or disclose any confidential information, including trade secrets, of any former employer or other person to whom Employee has an obligation of confidentiality. Rather, Employee will be
expected to use only that information which is generally known and used by persons with training and experience comparable to his own, which is common knowledge in the industry or otherwise legally in the public domain, or which is otherwise
provided or developed by the Company. Employee agrees that Employee will not bring onto Company premises any unpublished documents or property belonging to any former employer or other person to whom Employee has an obligation of confidentiality.
Employee hereby represents that he has disclosed to the Company any contract he has signed that may restrict his activities on behalf of the Company. 

12.    Return of Company Property. Upon the termination of Employee’s employment with the
Company for any reason, as a precondition to the receipt of the Accelerated Vesting, within five (5) days after Employee’s Separation from Service date (or earlier if requested by the Company), Employee will return to the Company all
Company documents (and all copies thereof) and other Company property within their possession, custody or control, including but not limited to Company files, notes, financial and operational information, customer lists and contact information,
investor and finance source lists and contract information, product information, research and development information, drawings, records, plans, forecasts, reports, payroll information, spreadsheets, studies, analyses, compilations of data,
proposals, agreements, sales and marketing information, personnel information, specifications, code, software, databases, computer-recorded information, tangible property and equipment (including but not limited to computers, facsimile machines,
mobile telephones, tablets, handheld devices and servers), credit cards, entry cards, identification badges and keys, and any materials of any kind which contain or embody any proprietary or confidential information of the Company (and all
reproductions thereof in 

 
whole or in part and in any medium). Employee shall deliver to the Board a signed statement certifying compliance with this Section 12 prior to the receipt of the Accelerated Vesting. 

13.    Exclusive Services. Employee shall at all times faithfully, industriously and to the best of
Employee’s ability, experience and talent perform to the satisfaction of the Board all of the duties that may be assigned to Employee hereunder and shall devote such portion of his productive time and efforts to the performance of such duties
as is required under this Agreement. Subject to the terms of the Confidential Information and Inventions Assignment Agreement, this shall not preclude Employee from devoting time to personal and family investments or serving on community and civic
boards, participating in industry associations, or engaging in other business or public activities (including providing consulting services to other entities, being employed by other entities and/or serving on the board of other entities), provided
such activities do not interfere with the duties to the Company, as determined in good faith by the Board. Notwithstanding the foregoing, during Employee’s employment by the Company, except on behalf of the Company, Employee will not directly
or indirectly serve as an officer, director, stockholder, employee, partner, proprietor, investor, joint venturer, associate, representative or consultant of any other person, corporation, firm, partnership or other entity whatsoever known by
Employee to compete with the Company (or is planning or preparing to compete with the Company) in the fields of respiratory syncytial virus and cytomegalovirus or any other vaccine indications then in development by the Company, anywhere in the
world; provided, however, that Employee may purchase or otherwise acquire up to (but not more than) one percent (1%) of any class of securities of any enterprise (but without participating in the activities of such enterprise) if such
securities are listed on any national or regional securities exchange. If the Board determines Employee is in breach of this Section 13, and provided such breach is not cured within thirty (30) days of written notification of such breach
from the Board, then the Company may terminate Employee’s employment for Cause. 

14.    Dispute Resolution. To ensure the rapid and economical resolution of disputes that may arise
in connection with Employee’s service or employment with the Company, Employee and the Company agree that any and all disputes, claims, or causes of action, in law or equity, including but not limited to statutory claims, arising from or
relating to the enforcement, breach, performance, or interpretation of this Agreement, Employee’s service or employment with the Company, or the termination of such service or employment, shall be resolved, to the fullest extent permitted by
law, by final, binding and confidential arbitration in the city of the Company’s then principal place of business in the United States conducted by JAMS or its successor, under the then applicable JAMS Arbitration Rules and Procedures for
Employment Disputes (available at http://www.jamsadr.com/rules-employment-arbitration/). Employee acknowledges that by agreeing to this arbitration procedure, he waives the right to resolve any such dispute
through a trial by jury or judge or administrative proceeding. Employee will have the right to be represented by legal counsel at any arbitration proceeding. The arbitrator shall: (a) have the authority to compel adequate discovery for the
resolution of the dispute and to award such relief as would otherwise be permitted by law; and (b) issue a written statement signed by the arbitrator regarding the disposition of each claim and the relief, if any, awarded as to each claim, the
reasons for the award, and the arbitrator’s essential findings and conclusions on which the award is based. The arbitrator shall be authorized to award all relief that Employee or the Company would be entitled to seek in a court of law. The
Company shall pay all JAMS arbitration fees in excess of the administrative fees that Employee would be required to pay if the dispute were decided in a court of law. The parties agree this arbitration agreement does not extend to claims for
workers’ compensation or unemployment benefits, or any other claims, that Employee cannot, as a matter of applicable law, be required to arbitrate, nor does it preclude Employee from initiating a complaint before the Equal Employment
Opportunity Commission or any other governmental agency, but if any such complaint is not resolved before the agency any action for money damages shall be submitted to arbitration pursuant to this paragraph. Nothing in this Agreement is intended to
prevent any party from obtaining injunctive relief in court to prevent irreparable harm pending the conclusion of any such arbitration. 

 15.    Miscellaneous. This Agreement,
together with the Confidential Information and Inventions Assignment Agreement and the other agreements referenced herein, forms the complete and exclusive statement governing Employee’s employment with the Company. It supersedes any other
agreements or promises made to Employee by anyone, whether oral or written, including, without limitation, the Prior Agreement. Changes in the terms of Employee’s employment, other than those changes expressly reserved to the Company’s or
the Board’s discretion in this Agreement, require a written modification approved by the Company and signed by a duly authorized officer of the Company. This Agreement will bind the heirs, personal representatives, successors and assigns of
Employee and the Company, and inure to the benefit of Employee and the Company, their heirs, successors and assigns. If any provision of this Agreement is determined to be invalid or unenforceable, in whole or in part, this determination shall not
affect any other provision of this Agreement and the provision in question shall be modified so as to be rendered enforceable in a manner consistent with the intent of the parties insofar as possible under applicable law. This Agreement shall be
construed and enforced in accordance with the laws of the State of Washington without regard to conflicts of law principles. Any ambiguity in this Agreement shall not be construed against any party as the drafter. Any waiver of a breach of this
Agreement, or rights hereunder, shall be in writing and shall not be deemed to be a waiver of any successive breach or rights hereunder. This Agreement may be executed in counterparts which shall be deemed to be part of one original, and facsimile
and electronic signatures shall be equivalent to original signatures. 

16.    Definitions. For purposes of this Agreement, the following terms shall have the
following meanings: 
 (a)    “Cause” shall mean the occurrence of any of the
following events, in each instance that has a material adverse impact on the Company or any successor or affiliate thereof as determined by the Board in its reasonable discretion: (a) Employee’s conviction of, or plea of “guilty”
or “no contest” to, any felony or any crime involving fraud, dishonesty or moral turpitude under the laws of the United States or any state thereof; (b) Employee’s commission of, or participation in, a fraud or act of dishonesty
or other illegal act against the Company; (c) Employee’s intentional, material violation of any contract or agreement between Employee and the Company or of any statutory duty owed to the Company; (d) Employee’s unauthorized use
or disclosure of the Company’s confidential information or trade secrets; or (e) gross misconduct; provided, that, with respect to (c) and (d) above, “Cause” will be triggered after Employee has received
written notification of such failure from the Board, which, if curable, remains uncured after thirty (30) days written notice from the Board. 

(b)    “Change in Control” shall mean (a) a merger or consolidation of the
Company with or into any other corporation or other entity or person, (b) a sale, lease, exchange or other transfer in one transaction or a series of related transactions of all or substantially all of the Company’s assets, or (c) any
other transaction, including the sale by the Company of new shares of its capital stock or a transfer of existing shares of capital stock of the Company, the result of which is that a third party that is not an affiliate of the Company or its
stockholders (or a group of third parties not affiliated with the Company or its stockholders) immediately prior to such transaction acquires or holds capital stock of the Company representing a majority of the Company’s outstanding voting
power immediately following such transaction; provided that the following events shall not constitute a “Change in Control”: (i) a transaction (other than a sale of all or substantially all of the Company’s assets) in which the
holders of the voting securities of the Company immediately prior to the merger or consolidation hold, directly or indirectly, at least a majority of the voting securities in the successor corporation or its parent immediately after the merger or
consolidation; (ii) a sale, lease, exchange or other transaction in one transaction or a series of related transactions of all or substantially all of the Company’s assets to an affiliate of the Company; (iii) an initial public
offering of any of the Company’s securities or any other transaction or series of related transactions principally for bona fide equity financing purposes; (iv) a reincorporation of the Company solely to change its jurisdiction; (v) a
transaction undertaken for the primary purpose of creating a holding 

 
company that will be owned in substantially the same proportion by the persons who held the Company’s securities immediately before such transaction; or (vi) a Qualified Funding Event.
Notwithstanding the foregoing, if a Change in Control would give rise to a payment or settlement event with respect to any payment or benefit that constitutes “nonqualified deferred compensation,” the transaction or event constituting the
Change in Control must also constitute a “change in control event” (as defined in Treasury Regulation §1.409A-3(i)(5)) in order to give rise to the payment or settlement event, to the extent
required by Section 409A. 
 (c)    “Founders Shares” shall mean those
shares issued to Employee pursuant to that certain Restricted Stock Purchase Agreement dated as of December 11, 2017, between the Company and The Adam K. and Maria M. Simpson Family Trust DTD 04/27/07, as amended from time to time. 

(d)    “Good Reason” shall mean any of the following actions taken without Cause
by the Company or a successor corporation or entity without Employee’s consent: (a) material reduction of Employee’s base compensation, other than to the extent the base compensation of all of the executive officers of the Company are
concurrently reduced by the same or greater percentage; (b) material reduction in Employee’s authority, duties or responsibilities, provided, however, that a change in job position (including a change in title) shall not be deemed a
“material reduction” unless Employee’s new authority, duties or responsibilities are materially reduced from the prior authority, duties or responsibilities; or (c) relocation of the principal place at which Employee is required
to provide services to the Company or Employee’s principal place of employment that results in an increase in Employee’s one-way driving distance by more than fifty (50) miles from
Employee’s then current principal place of business or residence, as applicable. In order to resign for Good Reason, Employee must provide written notice of the event giving rise to Good Reason to the Company within ninety (90) days after
the condition arises, allow the Company thirty (30) days to cure such condition, and if the Company fails to cure the condition within such period, then Employee’s resignation from all positions Employee then holds with the Company must be
effective not later than ninety (90) days after the end of the Company’s cure period. 

(e)    “Qualified Funding Event” shall mean any of the following: (a) an
equity financing with gross proceeds to the Company of at least $5,000,000.00 in which investors purchase any series of the Company’s Preferred Stock other than its Series 1 Preferred Stock; or (b) any option, phased acquisition, non-dilutive financing or similar transaction with gross proceeds to the Company of at least $5,000,000.00 granting a person or entity, or group of related persons or entities, the right to ultimately proceed with a
Sale Transaction. 
 (f)    “Sale Transaction” shall mean any of the following
transactions: (a) any consolidation or merger of the Company with or into any other corporation or other entity or person, or any other corporate reorganization, other than any such consolidation, merger or reorganization in which the shares of
capital stock of the Company immediately prior to such consolidation, merger or reorganization, continue to represent a majority of the voting power of the surviving entity (or, if the surviving entity is a wholly owned subsidiary, its parent)
immediately after such consolidation, merger or reorganization; (b) any transaction or series of related transactions to which the Company is a party in which in excess of fifty percent (50%) of the Company’s voting power is transferred,
excluding any transaction or series of transactions principally for bona fide equity financing purposes in which cash is received by the Company or any successor or indebtedness of the Company is cancelled or converted or a combination thereof; or
(c) any sale, lease, exclusive license or other disposition of the intellectual property or assets of the Company. 

(g)    “Separation from Service” shall mean a “separation from service”
as such term is defined in Treasury Regulation Section 1.409A-1(h). 

 (h)    “Stock Awards” shall mean
means all stock options, restricted stock and such other awards granted pursuant to the Company’s stock option and equity incentive award plans or agreements and any shares of stock issued upon exercise thereof, including the Founders Shares.

 (Signature Page Follows) 

 Sincerely, 

ICOSAVAX, INC. 
  

			
	 By:
	 	 /s/ Tadataka Yamada

		 	  Tadataka Yamada, Chairman of the Board

 ACKNOWLEDGED AND AGREED: 

 

	
	 /s/ Adam K. Simpson

	 Adam K. Simpson

 AMENDMENT TO 

AMENDED AND RESTATED EMPLOYMENT LETTER AGREEMENT 

This AMENDMENT TO AMENDED AND RESTATED EMPLOYMENT LETTER AGREEMENT (this “Amendment”) is made and entered
into effective as of February 10, 2021, by and between Icosavax, Inc. (the “Company”) and Adam K. Simpson (“Employee”). 

RECITALS 

WHEREAS, Employee and the Company previously entered into that certain Amended and Restated Employment Letter Agreement, dated
as of May 11, 2020 (the “Agreement”), pursuant to which Employee currently is employed by the Company; and 

WHEREAS, the Company and Employee wish to enter into this Amendment to modify certain terms of the Agreement. 

NOW, THEREFORE, in consideration of the mutual promises and covenants and the respective undertakings of the Company and
Employee set forth below, the Company and Employee agree as follows: 
 AGREEMENT 

1.    Amendment to Section 1. The penultimate sentence of Section 1 of the
Agreement is hereby amended to read as follows: 
 “Employee will be employed on a full-time basis.” 

2.    Amendment to Section 2(a). Section 2(a) of the Agreement is hereby
amended to read as follows: 
 “(a)    Salary. Employee’s base salary will be
$475,000.00 per year (the “Base Salary”), less payroll deductions and withholdings, paid on the Company’s normal payroll schedule.” 

3.    Amendment to Section 3. The first sentence of Section 3 of the
Agreement is hereby amended to read as follows: 
 “Employee will be eligible to earn an annual performance bonus of up
to fifty percent (50%) of Employee’s Base Salary rate (the “Annual Bonus”) for performance at “targeted” levels.” 

4.    Amendment to Section 13. The first sentence of Section 13 of the
Agreement is hereby amended to read as follows: 
 “Employee shall at all times faithfully, industriously and to the
best of Employee’s ability, experience and talent perform to the satisfaction of the Board all of the duties that may be assigned to Employee hereunder.” 

 5.    Status of Agreement. Except to the limited
extent expressly amended hereby, the Agreement and its terms and conditions remain in full force and effect and unchanged by this Amendment. Capitalized terms used herein but not defined herein shall have the meanings ascribed to such terms in the
Agreement. 
 6.    Duplicate Counterparts; Facsimile. This Amendment may be executed in
duplicate counterparts, each of which shall be deemed an original; provided, however, such counterparts shall together constitute only one agreement. Facsimile signatures or signatures sent via electronic mail shall be as effective as original
signatures. 
 [Signature page follows.] 

  
 1 

 IN WITNESS WHEREOF, the Parties have executed this Amendment as of the
date(s) set forth below. 
  

					
		 	 ICOSAVAX, INC.

			
	 Dated: February 19, 2021
	 	 By:
	 	 /s/ Tadataka Yamada

			
		 	 Name:
	 	 Tadataka Yamada

			
		 	 Title:
	 	 Chairman of the Board

		
		 	 EMPLOYEE

			
	 Dated: February 19, 2021
	 		 	 /s/ Adam K. Simpson

		 	 Adam K. Simpson

  
 2

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