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 Exhibit 4.2 
  

 
 BIOGEN INC., 

as Issuer 
 and 

U.S. Bank National Association, 

as Trustee 
 Second
Supplemental Indenture 
 Dated as of April 30, 2020 

 









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 TABLE OF CONTENTS 

 

					
	 	  	Page	 
	 ARTICLE I DEFINITIONS SECTION
	  	 	1	 
	 Section 1.1.    
Certain Terms Defined in the Indenture
	  	 	1	 
	
Section 1.2.    Definitions
	  	 	2	 
		
	 ARTICLE II FORM AND TERMS OF THE NOTES
	  	 	5	 
	 Section 2.1.    Form and
Dating
	  	 	5	 
	 Section 2.2.    Terms of the
Notes
	  	 	7	 
	 Section 2.3.    Optional
Redemption
	  	 	9	 
	 Section 2.4.    
Repurchase of Notes Upon a Change of Control
	  	 	10	 
	 Section 2.5.    Limitation on
Liens
	  	 	11	 
	 Section 2.6.    
Limitation on Sale and Leaseback Transactions
	  	 	12	 
	 Section 2.7.    
Exempted Liens and Sale and Leaseback Transactions
	  	 	13	 
	 Section 2.8.    Other
Amendments
	  	 	13	 
		
	 ARTICLE III MISCELLANEOUS
	  	 	13	 
		
	 Section 3.1.    
Trust Indenture Act Controls
	  	 	13	 
	 Section 3.2.    Governing
Law
	  	 	14	 
	 Section 3.3.    Multiple
Counterparts
	  	 	14	 
	 Section 3.4.    Severability
	  	 	14	 
	 Section 3.5.    Ratification
	  	 	14	 
	
Section 3.6.    Effectiveness
	  	 	14	 
	 Section 3.7.    Notices, Approvals,
etc
	  	 	14	 
		
	 EXHIBIT A Form of 2.250% Senior Note due 2030
	  	 	A-1	 
		
	 EXHIBIT B Form of 3.150% Senior Note due 2050
	  	 	B-1	 


  
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 SECOND SUPPLEMENTAL INDENTURE 

SUPPLEMENTAL INDENTURE (this “Second Supplemental Indenture”), dated as of April 30, 2020, between BIOGEN INC., a Delaware
corporation (the “Company”), and U.S. Bank National Association, a national association, as Trustee (the “Trustee”). 

RECITALS OF THE COMPANY 

WHEREAS, the Company and the Trustee executed and delivered an Indenture, dated as of September 15, 2015 (the “Indenture”), to
provide for the issuance by the Company from time to time of Securities to be issued in one or more Series as provided in the Indenture; 

WHEREAS, the issuance and sale of $1,500,000,000 aggregate principal amount of a new Series of the Securities of the Company designated as its
2.250% Senior Notes due May 1, 2030 (the “Notes due 2030”) and $1,500,000,000 aggregate principal amount of a new Series of the Securities of the Company designated as its 3.150% Senior Notes due May 1, 2050 (the “Notes due
2050” and, together with the Notes due 2030, the “Notes”) have been authorized by resolutions adopted by the Board of Directors of the Company; 

WHEREAS, the Company desires to issue and sell $3,000,000,000 aggregate principal amount of the Notes on the date hereof; 

WHEREAS, Sections 2.2 and 8.1 of the Indenture provide that the Company, when authorized by a Board Resolution, and the Trustee may amend or
supplement the Indenture to provide for the issuance of and to establish the form or terms and conditions of Securities of any Series as permitted by the Indenture; 

WHEREAS, the Company desires to establish the form, terms and conditions of the Notes; and 

WHEREAS, all things necessary to make this Second Supplemental Indenture a valid supplement to the Indenture according to its terms and the
terms of the Indenture have been done; 
 NOW, THEREFORE, for and in consideration of the premises stated herein and the purchase of the
Notes by the Holders thereof, the parties hereto hereby enter into this Second Supplemental Indenture, for the equal and proportionate benefit of all Holders of the Notes, as follows: 

ARTICLE I 

DEFINITIONS SECTION 
 
Section 1.1.    Certain Terms Defined in the Indenture. 
 For purposes of this Second Supplemental
Indenture, all capitalized terms used but not defined herein shall have the meanings ascribed to such terms in the Indenture, as amended hereby. 

  
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 Section 1.2.    Definitions. 

For the benefit of the Holders of the Notes, Section 1.1 of the Indenture shall be amended by adding the following new definitions: 

“Attributable Debt” means, with respect to a Sale and Leaseback Transaction, an amount equal to the lesser of (1) the fair
market value of the property (as determined in good faith by the Company’s board of directors); and (2) the present value of the total net amount of rent payments to be made under the lease during its remaining term, discounted at the rate
of interest set forth or implicit in the terms of the lease, compounded semi-annually. The calculation of the present value of the total net amount of rent payments is subject to adjustments specified in the indenture. 

“Change of Control” means the occurrence of any of the following: (1) the consummation of any transaction (including, without
limitation, any merger or consolidation) the result of which is that any “person” (as such term is used in Section 13(d) of the Exchange Act) (other than the Company or one of its Subsidiaries) becomes the beneficial owner (as defined
in Rules 13d-3 and 13d-5 under the Exchange Act), directly or indirectly, of more than 50% of the Voting Stock of the Company or other Voting Stock into which the Voting
Stock of the Company is reclassified, consolidated, exchanged or changed, measured by voting power rather than number of shares; provided, however, that a Person shall not be deemed beneficial owner of, or to own beneficially,
(A) any Securities tendered pursuant to a tender or exchange offer made by or on behalf of such Person or any of such Person’s Affiliates until such tendered Securities are accepted for purchase or exchange thereunder, or (B) any
Securities if such beneficial ownership (i) arises solely as a result of a revocable proxy delivered in response to a proxy or consent solicitation made pursuant to the applicable rules and regulations under the Exchange Act, and (ii) is
not also then reportable on Schedule 13D (or any successor schedule) under the Exchange Act; (2) the direct or indirect sale, transfer, conveyance or other disposition (other than by way of merger or consolidation), in one or more series
of related transactions, of all or substantially all of the assets of the Company and the assets of its Subsidiaries, taken as a whole, to one or more “persons” (as such term is used in Section 13(d) of the Exchange Act) (other than
to the Company or one of its Subsidiaries) (a “Transferee”), provided, however, that none of the circumstances in this clause (2) will be a Change of Control if the Persons that beneficially own the Company’s Voting
Stock immediately prior to the transaction own, directly or indirectly, shares representing a majority of the total Voting Stock as measured by voting power rather than number of shares of the Transferee; (3) the Company consolidates with, or
merges with or into, any “person” (as such term is used in Section 13(d) of the Exchange Act) or any such Person consolidates with, or merges with or into, the Company, in either case, pursuant to a transaction in which any of the
Company’s outstanding Voting Stock or the Voting Stock of such other Person is converted into or exchanged for cash, securities or other property, other than pursuant to a transaction in which shares of the Company’s Voting Stock
outstanding immediately prior to the transaction constitute, or are converted into or exchanged for, a majority of the Voting Stock of the surviving Person immediately after giving effect to such transaction; or (4) the adoption of a plan
relating to the Company’s liquidation or dissolution. 
 “Change of Control Triggering Event” means the occurrence of both a
Change of Control and a Rating Event. 

  
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 “Comparable Treasury Issue” means the U.S. Treasury security or securities
selected by an Independent Investment Banker as having an actual or interpolated maturity comparable to the remaining term of the Notes of the applicable Series (“Remaining Life”) to be redeemed that would be utilized, at the time of
selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of a comparable maturity to the remaining term of such Notes. 

“Comparable Treasury Price” means, with respect to any Notes of a Series on any Redemption Date, (A) the average of the
Reference Treasury Dealer Quotations for such Redemption Date, after excluding the highest and lowest such Reference Treasury Dealer Quotations, or (B) if the Independent Investment Banker obtains fewer than four such Reference Treasury Dealer
Quotations, the average of all such quotations. 
 “Consolidated Total Assets” means, with respect to any Person as of any date,
the amount of total assets as shown on the consolidated balance sheet of such Person for the most recent fiscal quarter for which financial statements have been filed with the Securities and Exchange Commission, prepared in accordance with
accounting principles generally accepted in the United States. 
 “Fitch” means Fitch Inc., or any successor thereto. 

“Global Notes” means, individually and collectively, each of the Notes in the form of Global Securities issued to DTC or its
nominee, substantially in the form of Exhibits A, B and C. 
 “Independent Investment Banker” means one of the Reference Treasury
Dealers appointed by the Company. 
 “Investment Grade Rating” means a rating equal to or higher than Baa3 (or the equivalent) by
Moody’s and BBB- (or the equivalent) by S&P or Fitch, and the equivalent investment grade credit rating from any additional rating agency or Rating Agencies selected by the Company. 

“Lien” means any pledge, mortgage, lien, encumbrance or other security interest. 

“Moody’s” means Moody’s Investors Service, Inc. or any successor thereto. 

“Par Call Date” means (1) with respect to the Notes due 2030, three months prior to the maturity date of the Notes due 2030 and
(2) with respect to the Notes due 2050, six months prior to the maturity date of the Notes due 2050. 
 “Principal Property”
means (1) any manufacturing facility, together with the land upon which it is erected and fixtures comprising a part thereof, owned or leased by the Company or any Subsidiary and located within the continental United States and having a net
book value which, on the date the determination as to whether a property is a Principal Property is being made, exceeds 1% of the Company’s Consolidated Total Assets other than any such facility or a portion thereof which the Company’s
board of directors determines in good faith, at any time on or prior to such date, is not of material importance to the total business conducted, or assets owned, by the Company and its Subsidiaries as an entirety or (2) any shares of stock or
Indebtedness of any Subsidiary owning a Principal Property. 

  
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 “Rating Agencies” means (1) each of Fitch, Moody’s and S&P and
(2) if any of Fitch, Moody’s and S&P ceases to rate the Notes or fails to make a rating of the Notes publicly available for reasons outside of the control of the Company, a “nationally recognized statistical rating
organization” within the meaning of Rule 15c3-1(c)(2)(vi)(F) under the Exchange Act selected by the Company (as certified by a resolution of the Board of Directors of the Company) and which is reasonably
acceptable to the Trustee as a replacement agency for Fitch, Moody’s or S&P, or all of them, as the case may be. 
 “Rating
Event” means with respect to any Series of Notes, the rating on such Notes is lowered by at least two of the three Rating Agencies and such Notes are rated below an Investment Grade Rating by at least two of the three Rating Agencies, on any
day during the period commencing on the earlier of the date of the first public notice of the occurrence of a Change of Control or the Company’s intention to effect a Change of Control and ending 60 days following consummation of such Change of
Control (which period will be extended so long as the rating of the applicable Series of Notes is under publicly announced consideration for a possible downgrade by any of the Rating Agencies). 

“Reference Treasury Dealer” means each of Goldman Sachs & Co. LLC, BofA Securities, Inc. and J.P. Morgan Securities LLC, or
their respective affiliates, which are primary U.S. Government securities dealers in The City of New York, and their respective successors plus three other primary U.S. Government securities dealers in The City of New York selected by the Company;
provided, however, that if any of the foregoing or their affiliates shall cease to be a primary U.S. Government securities dealer in The City of New York (a “Primary Treasury Dealer”), the Company will substitute therefor
another Primary Treasury Dealer. 
 “Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer
and any Redemption Date, the average, as determined by the Independent Investment Banker, of the bid and asked prices for the applicable Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to
the Trustee by the Reference Treasury Dealers at 3:30 p.m. New York time on the third Business Day preceding such Redemption Date. 

“Sale and Leaseback Transaction” means any arrangement with any Person providing for the leasing by the Company or any Subsidiary of
the Company of any property that has been or is to be sold or transferred by the Company or such Subsidiary, as the case may be, to such Person. 

“Subsidiary” of any Person means (1) a corporation, a majority of the outstanding voting stock of which is, at the time,
directly or indirectly, owned by such Person by one or more Subsidiaries of such Person, or by such Person and one or more Subsidiaries thereof or (2) any other Person (other than a corporation), including, without limitation, a partnership or
joint venture, in which such Person, one or more Subsidiaries thereof or such Person and one or more Subsidiaries thereof, directly or indirectly, at the date of determination thereof, has at least majority ownership interest entitled to vote in the
election of directors, managers or trustees thereof (or other Person performing similar functions). 

  
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 “S&P” means Standard & Poor’s Ratings Services, a
Standard & Poor’s Financial Services LLC business, or any successor thereto. 
 “Treasury Rate” means, with respect
to any Redemption Date: (1) the rate per annum equal to the yield, under the heading which represents the average for the immediately preceding week, appearing in the most recently published statistical release designated “H.15(519)”
or any successor publication which is published weekly by the Board of Governors of the Federal Reserve System and which establishes yields on actively traded U.S. Treasury securities adjusted to constant maturity under the caption “Treasury
Constant Maturities” for the maturity corresponding to the Comparable Treasury Issue; provided that, if no maturity is within three months before or after the Remaining Life of the Notes to be redeemed, yields for the two published
maturities most closely corresponding to the Comparable Treasury Issue shall be determined and the Treasury Rate shall be interpolated or extrapolated from those yields on a straight-line basis, rounding to the nearest month; or (2) if such
release (or any successor release) is not published during the week preceding the calculation date or does not contain such yields, the rate per year equal to the semiannual equivalent yield to maturity or interpolated (on a day count basis) of the
Comparable Treasury Issue, assuming a price for the applicable Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the applicable Comparable Treasury Price for such Redemption Date. The Treasury Rate shall be
calculated on the third business day preceding the Redemption Date. 
 “Voting Stock” means, with respect to any specified
“person” (as that term is used in Section 13(d) of the Exchange Act) as of any date, the capital stock of such person that is at the time entitled to vote generally in the election of the board of directors of such person. 

ARTICLE II 

FORM AND TERMS OF THE NOTES 
 
Section 2.1.    Form and Dating. 
 The Notes due 2030 and the Trustee’s certificate of
authentication shall be substantially in the form of Exhibit A attached hereto. The Notes due 2050 and the Trustee’s certificate of authentication shall be substantially in the form of Exhibit B attached hereto. The Notes shall be
executed on behalf of the Company by an Officer of the Company. The Notes may have notations, legends or endorsements required by law, stock exchange rules or usage. Each Note shall be dated the date of its authentication. The Notes and any
beneficial interest in the Notes shall be in minimum denominations of $2,000 and integral multiples of $1,000 in excess thereof. 
 The
terms and notations contained in the Notes shall constitute, and are hereby expressly made, a part of the Indenture as supplemented by this Second Supplemental Indenture and the Company and the Trustee, by their execution and delivery of this Second
Supplemental Indenture, expressly agree to such terms and provisions and to be bound thereby. 

  
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 (a)    Global Notes. The Notes of each Series designated herein
shall be issued initially in the form of one or more fully registered Global Securities, which shall be deposited on behalf of the purchasers of the Notes represented thereby with The Depository Trust Company, New York, New York (“DTC”)
and registered in the name of Cede & Co., DTC’s nominee, duly executed by the Company, authenticated by the Trustee and with guarantees endorsed thereon as hereinafter provided. The aggregate principal amount of outstanding Notes may
from time to time be increased or decreased by adjustments made on the records of the Trustee and DTC or its nominee as hereinafter provided. 

The Global Notes may not be transferred except by DTC, in whole and not in part, to another nominee of DTC or to a successor of DTC or its
nominee. If at any time DTC for the Notes notifies the Company that DTC is unwilling to continue as the depositary for the Global Notes or ceases to be a clearing agency, or if the Company so elects or if there is an Event of Default under the
Notes, then the Company shall execute, and the Trustee shall, upon receipt of a Company Order for authentication, authenticate and deliver, Definitive Notes in an aggregate principal amount equal to the principal amount of the Global Notes in
exchange for such Global Note, which DTC will distribute to its participants. 
 (b)    Book-Entry Provisions.
This Section 2.1(b) shall apply only to the Global Notes deposited with or on behalf of DTC. 
 The Company shall execute and the
Trustee shall, in accordance with this Section 2.1(b), authenticate and deliver the Global Notes that shall be registered in the name of DTC or the nominee of DTC and shall be delivered by the Trustee to DTC or pursuant to DTC’s
instructions. 
 Depositary participants shall have no rights either under the Indenture or with respect to any Global Notes held on their
behalf by DTC or under such Global Notes. DTC shall be treated by the Company, the Trustee and any agent of the Company or the Trustee as the absolute owner of such Global Note for all purposes under the Indenture. Notwithstanding the foregoing,
nothing herein shall prevent the Company or the Trustee from giving effect to any written certification, proxy or other authorization furnished by DTC or impair, as between DTC and the depositary participants, the operation of customary practices of
such DTC governing the exercise of the rights of an owner of a beneficial interest in the Global Notes. 

(c)    Definitive Notes. Notes issued in certificated form shall be substantially in the form of Exhibit A or
Exhibit B, as applicable, attached hereto, but without including the text referred to therein as applying only to Global Notes. Except as provided above in subsection (a), owners of beneficial interests in the Global Notes will not be entitled to
receive physical delivery of certificated Notes. 
 (d)    Transfer and Exchange of the Notes. The transfer and
exchange of beneficial interests in the Global Notes shall be effected through DTC, in accordance with the Indenture and the procedures of DTC therefor. Beneficial interests in the Global Notes may be transferred to Persons who take delivery thereof
in the form of a beneficial interest in the Global Notes. 
  

  
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 (e)    Paying Agent. The Company appoints the Trustee as the
initial agent of the Company for the payment of the principal of (and premium, if any) and interest on the Notes and the Corporate Trust Office of the Trustee in St. Paul, Minnesota, be and hereby is, designated as the office or agency where the
Notes may be presented for payment and where notices to or demands upon the Company in respect of the Notes and the Indenture pursuant to which the Notes are to be issued may be served. 

Section 2.2.    Terms of the Notes. 

The following terms relating to the Notes are hereby established: 

(a)    Title. The Notes due 2030 shall constitute a Series of Securities having the title “2.250% Senior Notes
due 2030” and the Notes due 2050 shall constitute a separate Series of Securities having the title “3.150% Senior Notes due 2050”. 

(b)    Principal Amount. The aggregate principal amount of the Notes due 2030 that may be initially authenticated
and delivered under the Indenture (except for Notes due 2030 authenticated and delivered upon registration of, transfer of, or in exchange for, or in lieu of, other Notes due 2030 pursuant to Sections 2.7, 2.8, 2.11, 3.6 or 8.5 of the Indenture)
shall be $1,500,000,000. The aggregate principal amount of the Notes due 2050 that may be initially authenticated and delivered under the Indenture (except for Notes due 2050 authenticated and delivered upon registration of, transfer of, or in
exchange for, or in lieu of, other Notes due 2050 pursuant to Sections 2.7, 2.8, 2.11, 3.6 or 8.5 of the Indenture) shall be $1,500,000,000. The Company may from time to time, without the consent of the Holders of Notes of any Series, issue
additional Notes (in any such case “Additional Notes”) of any Series having the same ranking and the same interest rate, maturity and other terms as the Notes of that Series. Any additional Notes of a Series and the existing Notes of that
Series will constitute a single Series under the Indenture and all references to the relevant Notes shall include the Additional Notes unless the context otherwise requires; provided, that if the Additional Notes of any Series are not
fungible with the Notes of such Series for U.S. federal income tax purposes, the Additional Notes will have a separate CUSIP number. 

(c)    Issuance Price. The Notes due 2030 shall be issued at a price to the public of 99.973% of the principal
amount of such Series and the Notes due 2050 shall be issued at a price to the public of 99.174% of the principal amount of such Series, plus, in each case, accrued interest, if any, from April 30, 2020 to the Original Issue Date (as defined in
the Note of the applicable Series). 
 (d)    Maturity Date. The entire outstanding principal of the Notes due
2030 shall be payable on May 1, 2030 and the entire outstanding principal of the Notes due 2050 shall be payable on May 1, 2050. 

(e)    Interest Rate; Place and Method of Payment. The rate at which the Notes due 2030 shall bear interest shall
be 2.250% per annum and the rate at which the Notes due 2050 shall bear interest shall be 3.150% per annum; the date from which interest shall accrue on the Notes shall be April 30, 2020, or the most recent Interest Payment Date to which
interest has been paid or provided for; the Interest Payment Dates for the Notes shall be November 1 and May 1 of each year, beginning November 1, 2020; the interest so payable, and punctually paid or duly provided for, on any
Interest Payment Date, will be paid, in immediately available funds, to 

  
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the Persons in whose names the Notes (or one or more predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be October 15 or
April 15, as the case may be, next preceding such Interest Payment Date. Any such interest not punctually paid or duly provided for shall forthwith cease to be payable to the respective Holders on such Regular Record Date, and such defaulted
interest, may be paid to the Persons in whose names the Notes (or one or more predecessor Securities) is registered at the close of business on a special record date for the payment of such defaulted interest to be fixed by the Trustee, notice
whereof shall be given to Holders of Notes not less than 15 days prior to such special record date, or may be paid at any time in any other lawful manner not inconsistent with requirements of any securities exchange on which the Notes may be listed,
and upon such notice as may be required by such exchange, all as more fully provided in said Indenture. Payment of principal and interest on this Note will be made at the Corporate Trust Office of the Trustee or such other office or agency of the
Company as may be designated for such purpose, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts; provided, however, that each installment of
interest and principal on the Notes may at the Company’s option be paid in immediately available funds by transfer to an account maintained by the payee located in the United States. 

(f)    Optional Redemption. The Notes of each Series are redeemable at the option of the Company on the terms and
conditions described in Section 2.3 hereof. 
 (g)    Sinking Fund Obligation. There is no sinking fund
obligation. 
 (h)    Mandatory Redemption or Repurchase. The Company shall be required to make an offer to
repurchase the Notes of any Series upon the occurrence of a Change of Control Triggering Event on the terms and conditions described in Section 2.4 hereof. 

(i)    Form and Denomination of Notes. The Notes of each Series shall be issued in registered form in the
denominations specified in Section 2.1 hereof. 
 (j)    Principal Payable Upon Acceleration. The entire
principal amount of, and premium, if any, on all the Notes of any Series then outstanding is payable upon acceleration of such Notes in accordance with Section 6.2 of the Indenture. 

(k)    Currency. The currency of denomination of the Notes is United States Dollars. Payment of principal of and
interest and premium, if any, on the Notes will be made in United States Dollars. 
 (l)    Payment Not Made by
Reference to Index. Payments of principal of or interest or premium, if any, on the Notes of any Series shall not be determined by reference to any index. 

(m)    Notes Unsecured. Except as otherwise required pursuant to Section 2.5 hereof, the Notes are not secured
by any collateral. 
 (n)    Additional/Different Covenants. In addition to the covenants set forth in Indenture,
the Company shall be subject to the obligations set forth in Sections 2.3, 2.4, 2.5, 2.6 and 2.7 hereof. 

  
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 (o)    Modification to Events of Default. There is no addition
to, deletion of or change in (i) any Events of Default as applicable to the Notes of any Series as set forth under the Indenture or (ii) the right of the Trustee or the requisite Holders of any Series of Notes to declare the principal
amount thereof due and payable pursuant to Section 6.2 of the Indenture. 
 (p)    Conversion. No Notes of
any Series are convertible or exchangeable for shares of common stock or preferred stock of the Company. 

(q)    Depositories and Agents. The Notes of each Series shall be deposited with The Depository Trust Company,
acting as depositary, as described in Section 2.1(a) hereof. The Company appoints the Trustee as initial paying agent for the Notes as described in Section 2.1(e) hereof. There is no interest rate calculation agent, exchange rate
calculation agent or other agent with respect to the Notes of any Series other than those appointed herein. 

(r)    Subordination. The Notes are not subordinated in right of payment to any other unsecured Indebtedness of the
Company. 
 (s)    Defeasance. The Notes of any Series are defeasible pursuant to Article 9 of the Indenture.

 Section 2.3.    Optional Redemption. 

(a)    The provisions of Article 3 of the Indenture shall apply to the Notes, except that, solely with respect to the
Notes, the third sentence of Section 3.1 of the Indenture shall be substituted with the following: 
 “If a Series of Securities
is redeemable and the Company elects to redeem such Securities of a Series, it shall notify the Trustee of the Redemption Date and the principal amount of Securities to be redeemed at least 15 days (unless a shorter notice period shall be
satisfactory to the Trustee) before the Redemption Date.” 
 (b)    At any time prior to the Par Call Date
applicable to a Series of Notes, from time to time, the Notes are redeemable, as a whole or in part, at the Company’s option, on at least 10 days, but not more than 60 days, prior notice mailed to the registered address of each Holder of the
Notes to be redeemed (or otherwise delivered in accordance with the applicable procedures of DTC), at a redemption price equal to the greater of: (i) 100% of principal amount of the Notes to be redeemed, or (ii) the sum of the present values of
the remaining scheduled payments (through the Par Call Date assuming for such purpose that such Notes matured on the applicable Par Call Date) of interest and principal thereon (exclusive of interest accrued and unpaid to, but not including, the
date of redemption) discounted to the date of redemption on a semiannual basis, assuming a 360-day year consisting of twelve 30-day months, at the Treasury Rate plus 25
basis points, in the case of Notes due 2030, and 30 basis points, in the case of Notes due 2050, plus, in either case, accrued and unpaid interest to, but not including, the date of redemption. 

(c)    In addition, at any time on or after the Par Call Date applicable to a Series of Notes, the Notes may be redeemed,
as a whole or in part, at the Company’s option, on at least 10 days, but not more than 60 days, prior notice mailed to the registered address of each Holder of the Notes to be redeemed (or otherwise delivered in accordance with the applicable
procedures of DTC), at a redemption price equal to 100% of the principal amount of the Notes to be redeemed on the Redemption Date plus accrued and unpaid interest to, but not including, the date of redemption.


  
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 (d)    On and after the Redemption Date for the Notes of any Series,
interest will cease to accrue on the Notes of such Series or any portion thereof called for redemption, unless the Company defaults in the payment of the redemption price. On or before the Redemption Date for the Notes of such Series, the Company
will deposit with a Paying Agent, or the Trustee, funds sufficient to pay the redemption price of the Notes to be redeemed on such date. If less than all of the Notes of a Series are to be redeemed, the Notes of that Series to be redeemed will be
selected by DTC in accordance with its standard procedures. If the Notes to be redeemed are not global notes then held by DTC, or DTC prescribes no method of selection, the Trustee will select the Notes to be redeemed on a pro rata basis, by lot, or
by any other method the Trustee deems fair and appropriate and subject to and otherwise in accordance with the procedures of DTC. Any redemption or notice of redemption may, at the Company’s discretion, be subject to one or more conditions
precedent, and, at the Company’s discretion, the Redemption Date may be delayed until such time as any or all such conditions shall be satisfied. The Company will provide written notice to the Trustee prior to the close of business two Business
Days prior to the Redemption Date if any such redemption has been rescinded or delayed, and upon receipt the Trustee shall provide such notice to each Holder of the Notes in the same manner in which the notice of redemption was given. 

Section 2.4.    Repurchase of Notes Upon a Change of Control. 

(a)    If a Change of Control Triggering Event occurs with respect to the Notes of a Series, unless the Company has
exercised its option to redeem the Notes of such Series as described above, the Company will be required to make an offer (the “Change of Control Offer”) to each Holder of the Notes of such Series to repurchase all or any part (equal to
$2,000 or an integral multiple of $1,000 in excess thereof) of that Holder’s Notes of such Series on the terms set forth in such Notes. In the Change of Control Offer, the Company will be required to offer payment in cash equal to 101% of the
aggregate principal amount of Notes repurchased, plus accrued and unpaid interest, if any, on the Notes repurchased to but not including the date of repurchase (the “Change of Control Payment”). With respect to the Notes of each Series,
within 30 days following any Change of Control Triggering Event or, at the Company’s option, prior to any Change of Control, but after public announcement of the transaction that constitutes or may constitute the Change of Control, a notice
will be mailed (or otherwise delivered in accordance with the applicable procedures of DTC) to Holders of the Notes of the applicable Series describing the transaction that constitutes or may constitute the Change of Control Triggering Event and
offering to repurchase the Notes of such Series on the date specified in the notice, which date will be no earlier than 10 days and no later than 60 days from the date such notice is mailed (or otherwise delivered in accordance with the applicable
procedures of DTC) or, if the notice is mailed (or otherwise delivered) prior to the Change of Control, no earlier than 10 days and no later than 60 days from the date on which the Change of Control Triggering Event occurs (the “Change of
Control Payment Date”). The notice will, if mailed (or otherwise delivered) prior to the date of consummation of the Change of Control, state that the offer to purchase is conditioned on the Change of Control Triggering Event occurring on or
prior to the Change of Control Payment Date. 

  
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 (b)    On the Change of Control Payment Date, the Company shall, to the
extent lawful: 
 (1)    accept for payment all Notes or portions of Notes properly tendered pursuant to the Change of
Control Offer; 
 (2)    deposit with the Paying Agent an amount equal to the Change of Control Payment in respect of
all Notes or portions of Notes properly tendered; and 
 (3)    deliver or cause to be delivered to the Trustee the
Notes properly accepted together with an Officers’ Certificate stating the aggregate principal amount of Notes or portions of Notes being repurchased. 

(c)    The Company shall not be required to make a Change of Control Offer upon the occurrence of a Change of Control
Triggering Event if a third party makes such an offer in the manner, at the times and otherwise in compliance with the requirements for an offer made by the Company and the third party repurchases all Notes properly tendered and not withdrawn under
its offer. In addition, the Company shall not repurchase any Notes if there has occurred and is continuing on the Change of Control Payment Date an Event of Default under the Indenture, other than an Event of Default arising as a result of a default
in the payment of the Change of Control Payment upon a Change of Control Triggering Event. 
 (d)    The Company shall
comply in all material respects with the requirements of Rule 14e-1 under the Exchange Act and any other securities laws and regulations thereunder to the extent such laws and regulations are applicable in
connection with the repurchase of the Notes as a result of a Change of Control Triggering Event. To the extent that the provisions of any such securities laws or regulations conflict with the Change of Control Offer provisions of the Notes, the
Company shall comply with the applicable securities laws and regulations and shall not be deemed to have breached its obligations under the Change of Control Offer provisions of the Notes by virtue of any such conflict. 

Section 2.5.    Limitation on Liens. 

For the benefit of the Holders of the Notes, a new Section 4.7 shall be added to the Indenture as follows: 

“Other than as provided in Section 4.9, the Company shall not, and shall not permit any Subsidiaries of the Company to, create or
assume any Indebtedness secured by any Lien on any of the Company’s or such Subsidiary’s respective Principal Properties unless the Notes are secured by such Lien equally and ratably with, or prior to, the Indebtedness secured by such
Lien. This restriction does not apply to Indebtedness that is secured by (i) Liens existing on the date of the issuance of the Notes; (ii) Liens securing only the Notes; (iii) Liens on property or shares of stock in respect of
Indebtedness of a Person existing at the time such Person becomes a Subsidiary of the Company or is merged into or consolidated with, or its assets are acquired by, the Company or any Subsidiary of the Company (provided that such Lien was not
incurred in anticipation of such transaction and was in existence prior to such transaction) so long as such 

  
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Lien does not extend to any other property and the Indebtedness so secured is not increased; (iv) Liens to secure Indebtedness incurred for the purpose of all or any part of a
property’s purchase price or cost of construction or additions, repairs, alterations, or other improvements; provided that (1) the principal amount of any Indebtedness secured by such Lien does not exceed 100% of such
property’s purchase price or cost, (2) such Lien does not extend to or cover any other property other than the property so purchased, constructed or on which such additions, repairs, alterations or other improvements were so made, and
(3) such Lien is incurred prior to or within 270 days after the acquisition of such property or the completion of construction or such additions, repairs, alterations or other improvements and the full operation of such property thereafter;
(v) Liens in favor of the United States or any state thereof, or any instrumentality of either, to secure certain payments pursuant to any contract or statute; (vi) Liens for taxes or assessments or other governmental charges or levies
which are not overdue for a period exceeding 60 days unless such Liens are being contested in good faith and for which adequate reserves are being maintained, to the extent required by generally accepted accounting principles; (vii) title
exceptions, easements, licenses, leases and other similar Liens that are not consensual and that do not materially impair the use of the property subject thereto; (viii) Liens to secure obligations under worker’s compensation laws,
unemployment compensation, old-age pensions and other social security benefits or similar legislation; (ix) Liens arising out of legal proceedings, including Liens arising out of judgments or awards;
(x) warehousemen’s, materialmen’s, carrier’s, landlord’s and other similar Liens for sums not overdue for a period exceeding 60 days unless such Liens are being contested in good faith and for which adequate reserves are
being maintained, to the extent required by generally accepted accounting principles; (xi) Liens incurred to secure the performance of statutory obligations, surety or appeal bonds, performance or return-of-money bonds, insurance, self-insurance or other obligations of a like nature incurred in the ordinary course of business; (xii) Liens that are rights of
set-off relating to the establishment of depository relations with banks not given in connection with the issuance of Indebtedness; (xiii) Liens arising out of conditional sale, title retention,
consignment or similar arrangements for the sale of goods entered into by the Company or any of its Subsidiaries in the ordinary course of business; (xiv) Liens in favor of the Company or the favor of any of its Subsidiaries; or (xv) Liens
to secure any extension, renewal, refinancing or refunding (or successive extensions, renewals, refinancings or refundings), in whole or in part, of any Indebtedness secured by Liens referred to in clauses (i) to (xv) or Liens created in
connection with any amendment, consent or waiver relating to such Indebtedness, so long as such Lien does not extend to any other Principal Property and the Indebtedness so secured does not exceed the fair market value (as determined by the
Company’s board of directors) of the assets subject to such Liens at the time of such extension, renewal, refinancing or refunding, or such amendment, consent or waiver, as the case may be.” 

Section 2.6.    Limitation on Sale and Leaseback Transactions. 

For the benefit of the Holders of the Notes a new Section 4.8 shall be added to the Indenture as follows: 

“Other than as provided under Section 4.9, the Company shall not, and shall not permit any of its Subsidiaries to, enter into any
Sale and Leaseback Transaction with respect to any of the Company’s or such Subsidiary’s respective Principal Properties, the acquisition or completion of construction and commencement of full operations of which has occurred more


  
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than 270 days prior thereto, unless (i) such transaction is entered into prior to the first issue date of the Notes; (ii) such transaction is for the sale and leasing back to the
Company of any property by one of its Subsidiaries; (iii) the Company or such Subsidiary is entitled to incur Indebtedness secured by a mortgage on the property to be leased in an amount equal to the Attributable Debt with respect to such Sale
and Leaseback Transaction without equally and ratably securing the Notes pursuant to the first sentence of Section 4.7; (iv) the lease is for a period not in excess of five years, including renewal rights; or (v) the Company or the
Subsidiary, prior to or within 270 days after the sale of such property in connection with the Sale and Leaseback Transaction is completed, applies the net cash proceeds of the sale of the property leased to (1) the retirement of the Notes or
debt of the Company ranking equally with the Notes or to the retirement of any debt of a Subsidiary of the Company, or (2) the acquisition of another Principal Property.” 

Section 2.7.    Exempted Liens and Sale and Leaseback Transactions. 

For the benefit of the Holders of the Notes a new Section 4.9 shall be added to the Indenture as follows: 

“Notwithstanding the restrictions described under Sections 4.7 or 4.8, the Company or any Subsidiary of the Company may create or assume
any Liens or enter into any Sale and Leaseback Transactions not otherwise permitted as described above, if the sum of the following does not exceed 15% of Consolidated Total Assets (i) the outstanding Indebtedness secured by such Liens (not
including any Liens permitted under Section 4.7 which amount does not include any Liens permitted under the provisions of this Section 4.9); plus (ii) all Attributable Debt in respect of such Sale and Leaseback Transaction entered
into (not including any Sale and Leaseback Transactions permitted under Section 4.8 which amount does not include any Sale and Leaseback Transactions permitted under the provisions of this Section 4.9), measured, in each case, at the time
such Lien is incurred or any such Sale and Leaseback Transaction is entered into by the Company or such Subsidiary of the Company.” 
 
Section 2.8.    Other Amendments. 
 For the benefit of the Holders of the Notes Section 2.3 of the
Indenture shall be amended by amending and restating the first paragraph of such Section in its entirety as follows: 
 “The Securities
shall be executed on behalf of the Company by an Officer of the Company. Such signature may be either manual or facsimile.” 
 
ARTICLE III 
 MISCELLANEOUS 
 
Section 3.1.    Trust Indenture Act Controls. 
 If any provision of this Second Supplemental Indenture
limits, qualifies or conflicts with another provision which is required to be included in this Second Supplemental Indenture by the TIA, the required provision shall control. If any provision of this Second Supplemental Indenture modifies or
excludes any provision of the TIA which may be so modified or excluded, the latter provision shall be deemed to apply to this Second Supplemental Indenture as so modified or to be excluded, as the case may be.


  
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 Section 3.2.    Governing Law. 

This Second Supplemental Indenture and the Notes shall be governed by and construed in accordance with the laws of the State of New York. 

Section 3.3.    Multiple Counterparts. 

The parties may sign multiple counterparts of this Second Supplemental Indenture. Each signed counterpart shall be deemed an original, but all
of them together represent one and the same Second Supplemental Indenture. 

Section 3.4.    Severability. 

Each provision of this Second Supplemental Indenture shall be considered separable and if for any reason any provision which is not essential
to the effectuation of the basic purpose of this Second Supplemental Indenture or the Notes shall be invalid, illegal or unenforceable, the validity, legality and enforceability of the remaining provisions shall not in any way be affected or
impaired thereby and a Holder shall have no claim therefor against any party hereto. 

Section 3.5.    Ratification. 

The Indenture, as supplemented and amended by this Second Supplemental Indenture, is in all respects ratified and confirmed. The Indenture and
this Second Supplemental Indenture shall be read, taken and construed as one and the same instrument. All provisions included in this Second Supplemental Indenture supersede any conflicting provisions included in the Indenture unless not permitted
by law. The Trustee accepts the trusts created by the Indenture, as supplemented by this Second Supplemental Indenture, and agrees to perform the same upon the terms and conditions of the Indenture, as supplemented by this Second Supplemental
Indenture. 
 Section 3.6.    Effectiveness. 

The provisions of this Second Supplemental Indenture shall become effective as of the date hereof. 

Section 3.7.    Notices, Approvals, etc. 

Notices, approvals, consents, requests and any communications hereunder must be in writing (provided that any communication sent to the
Trustee hereunder must be in the form of a document that is signed manually or by way of a digital signature provided by Adobe or DocuSign (or such other digital signature provider as specified in writing to the Trustee by the authorized
representative), in English. The Company agrees to assume all risks arising out of the use of digital signatures and electronic methods to submit communications to the Trustee, including without limitation the risk of the Trustee acting on
unauthorized instructions, and the risk of interception and misuse by third parties. 

  
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 IN WITNESS WHEREOF, the parties hereto have caused this Second Supplemental Indenture to be
duly executed as of the date first above written. 
 BIOGEN INC. 

By: /s/ Michael
Dambach                     

Name: Michael Dambach 

Title:    Vice President, Treasurer 

U.S. BANK NATIONAL ASSOCIATION, as Trustee 

By: /s/ Laura S. Cawley       

Name: Laura S. Cawley 

Title:    Vice President 

  
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 EXHIBIT A 

FORM OF 2.250% SENIOR NOTE DUE 2030 

THIS NOTE IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF DTC OR A NOMINEE
OF DTC. THIS NOTE IS EXCHANGEABLE FOR NOTES REGISTERED IN THE NAME OF A PERSON OTHER THAN DTC OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY DTC TO A NOMINEE OF DTC, BY A
NOMINEE OF DTC TO DTC OR ANOTHER NOMINEE OF DTC OR BY DTC OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH A SUCCESSOR DEPOSITARY. 

UNLESS THIS GLOBAL SECURITY IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION
(“DTC”), TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY GLOBAL SECURITY ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF
DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN. 
 BIOGEN INC. 

2.250% Senior Note due 2030 
  

 

			
	 REGISTERED
	 	 PRINCIPAL AMOUNT

	 No. Specimen
	 	 $ [ ]

		 	
	 CUSIP: [ ]
	 	
	 ISIN: [ ]
	 	

 Biogen Inc., a Delaware corporation (herein called the “Company,” which term includes any successor
Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., or registered assigns, the principal sum of $[ ] on May 1, 2030 (the “Maturity Date”) (except to the extent
redeemed or repaid prior to the Maturity Date) and to pay interest thereon from April 30, 2020 (the “Original Issue Date”) or from the most recent Interest Payment Date to which interest has been paid or duly provided for
semi-annually at the rate of 2.250% per annum, on November 1 and May 1 (each such date, an “Interest Payment Date”), commencing November 1, 2020, until the principal hereof is paid or made available for payment. 

  
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 Payment of Interest. The interest so payable, and punctually paid or made available
for payment, on any Interest Payment Date, will, as provided in the Indenture, be paid, in immediately available funds, to the Person in whose name this Note (or one or more Predecessor Securities) is registered at the close of business on
October 15 or April 15 (whether or not a Business Day, as defined in the Indenture), as the case may be, next preceding such Interest Payment Date (the “Regular Record Date”). Any such interest not punctually paid or duly
provided for (“Defaulted Interest”) will forthwith cease to be payable to the Holder on such Regular Record Date, and such Defaulted Interest, may be paid to the Person in whose name this Note (or one or more Predecessor Securities) is
registered at the close of business on a special record date (the “Special Record Date”) for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Notes not less than fifteen days
prior to such Special Record Date, or may be paid at any time in any other lawful manner not inconsistent with requirements of any securities exchange on which the Notes may be listed, and upon such notice as may be required by such exchange, all as
more fully provided in said Indenture. 
 Place of Payment. Payment of principal, premium, if any, and interest on this Note will be
made at the Corporate Trust Office of the Trustee or such other office or agency of the Company as may be designated for such purpose, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of
public and private debts; provided, however, that each installment of interest, premium, if any, and principal on this Note may at the Company’s option be paid in immediately available funds by transfer to an account maintained by
the payee located in the United States. 
 Time of Payment. In any case where any Interest Payment Date, the Maturity Date or any
date fixed for redemption or repayment of the Notes shall not be a Business Day, then (notwithstanding any other provision of the Indenture or this Note), payment of principal or interest, if any, need not be made on such date, but may be made on
the next succeeding Business Day with the same force and effect as if made on such Interest Payment Date, the Maturity Date or the date so fixed for redemption or repayment, and no interest shall accrue in respect of the delay. 

General. This Note is one of a duly authorized issue of Securities of the Company, issued and to be issued in one or more Series under
an indenture, dated as of September 15, 2015 (the “Base Indenture”), between the Company and U.S. Bank National Association (herein called the “Trustee,” which term includes any successor trustee under the Indenture with
respect to a Series of which this Note is a part), as supplemented by a Second Supplemental Indenture thereto, dated as of April 30, 2020 (the “Second Supplemental Indenture” and, together with the Base Indenture, the
“Indenture”). Reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities, and of the terms upon
which the Securities are, and are to be, authenticated and delivered. This Note is one of a duly authorized Series of Securities designated as “2.250% Senior Notes due 2030” (collectively, the “Notes”), initially limited in
aggregate principal amount to $1,500,000,000. 
 Further Issuance. The Company may from time to time, without the consent of the
Holders of the Notes, issue additional Securities (the “Additional Securities”) of this Series having the same ranking and the same interest rate, maturity and other terms as the Notes. Any Additional Securities of this Series and the
Notes will constitute a single Series under the Indenture and all references to the Notes shall include the Additional Securities unless the context otherwise requires. 

  
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 Events of Default. If an Event of Default with respect to the Notes shall have
occurred and be continuing, the principal of the Notes may be declared due and payable in the manner and with the effect provided in the Indenture. 

Sinking Fund. The Notes are not subject to any sinking fund. 

Optional Redemption. The Notes will be redeemable at any time, at the option of the Company, in whole or from time to time in part,
upon not less than 10 nor more than 60 days’ prior notice, on any date prior to their Maturity at a redemption price, calculated pursuant to the Indenture, which includes accrued interest thereon, if any, to, but not including, the Redemption
Date. In the case of any partial redemption, selection of the Notes for redemption will be made by the Trustee by such methods, as the Trustee in its sole discretion shall deem fair and appropriate. If any Note is to be redeemed in part only, the
notice of redemption relating to such Note shall state the portion of the principal amount thereof to be redeemed. A new Note in principal amount equal to the unredeemed portion thereof will be issued in the name of the Holder thereof upon
cancellation of this Note. 
 Repurchase upon a Change of Control Triggering Event. Upon the occurrence of a Change of Control
Triggering Event with respect to the Notes, the Company shall be required to make an offer to repurchase the Notes on the terms set forth in the Indenture. 

Defeasance and Covenant Defeasance. The Indenture contains provisions for defeasance at any time of (a) the entire indebtedness of
the Company on this Note and (b) certain restrictive covenants and the related Defaults and Events of Default, upon compliance by the Company with certain conditions set forth therein, which provisions apply to this Note. 

Modification and Waivers; Obligations of the Company Absolute. The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each Series. Such amendment may be effected under the Indenture at any time by the Company, and the Trustee with
the consent of the Holders of not less than a majority in aggregate principal amount of the outstanding Notes of each Series affected thereby. The Indenture also contains provisions permitting the Holders of not less than a majority in aggregate
principal amount of the Securities at the time outstanding, on behalf of the Holders of all outstanding Securities, to waive compliance by the Company with certain provisions of the Indenture. Furthermore, provisions in the Indenture permit the
Holders of not less than a majority in aggregate principal amount of the outstanding Securities of individual Series to waive on behalf of all of the Holders of Securities of such individual Series certain past defaults under the Indenture and their
consequences. Any such consent or waiver shall be conclusive and binding upon the Holder of this Note and upon all future Holders of this Note and of any Note issued upon the registration of transfer hereof or in exchange hereof or in lieu hereof,
whether or not notation of such consent or waiver is made upon this Note. 

  
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 No reference herein to the Indenture and no provision of this Note or of the Indenture shall
alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and interest on this Note at the time, place, and rate, and in the coin or currency, herein prescribed. 

Limitation on Suits. As set forth in, and subject to, the provisions of the Indenture, no Holder of any Note will have any right to
institute any proceeding with respect to the Indenture or for any remedy thereunder, unless such Holder shall have previously given to the Trustee written notice of a continuing Event of Default with respect to this Series, the Holders of not less
than 25% in aggregate principal amount of the outstanding Notes shall have made written request, and offered indemnity and/or security, to the Trustee to institute such proceedings as trustee, and the Trustee shall not have received from the Holders
of a majority in principal amount of the outstanding Notes a direction inconsistent with such request and shall have failed to institute such proceeding within 60 days; provided, however, that such limitations do not apply to a suit
instituted by the Holder hereof for the enforcement of payment of the principal of or interest on this Note on or after the respective due dates expressed herein. 

Authorized Denominations. The Notes are issuable only in registered form without coupons in denominations of $2,000 or any integral
multiple of $1,000 in excess thereof. 
 Registration of Transfer or Exchange. As provided in the Indenture and subject to certain
limitations herein and therein set forth, the transfer of this Note is registrable in the register of the Notes maintained by the Registrar upon surrender of this Note for registration of transfer, at the office or agency of the Company in any place
where the principal of and interest on this Note are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Registrar, duly executed by the Holder hereof or his attorney duly
authorized in writing, and thereupon one or more new Notes, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees. 

As provided in the Indenture and subject to certain limitations herein and therein set forth, the Notes are exchangeable for a like aggregate
principal amount of Notes of different authorized denominations, as requested by the Holders surrendering the same. 
 No service charge
shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith. 

Prior to due presentment of this Note for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may
treat the Holder as the owner hereof for all purposes, whether or not this Note be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary. 

Defined Terms. All terms used in this Note, which are defined in the Indenture and are not otherwise defined herein, shall have the
meanings assigned to them in the Indenture. 
 Governing Law. This Note shall be governed by and construed in accordance with the
laws of the State of New York. 

  
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 Unless the certificate of authentication hereon has been executed by the Trustee by manual
signature, this Note shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose. 
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page intentionally left blank.] 

  
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 IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed and its seal
to be hereunto affixed. 
  

			
	Dated: April [ ], 2020	 	
		
		 	 BIOGEN INC.

		 	  
 By:
——————————

		 	 Name:

		 	 Title:



  
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 TRUSTEE’S CERTIFICATE OF AUTHENTICATION 

This is one of the Notes of the Series designated and referred to in the within-mentioned Indenture, as such is supplemented by the
within-mentioned Second Supplemental Indenture. 
  

			
		 	 U.S. BANK NATIONAL ASSOCIATION, as Trustee

 

		
		 	  
 By: __________________________

		 	 Name:

	Dated: April [ ], 2020	 	 Title:



  
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 ASSIGNMENT 

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto 

	
	 
	 

 PLEASE INSERT SOCIAL SECURITY NUMBER OR OTHER IDENTIFYING NUMBER OF ASSIGNEE 

 

	
	 

  

	
	  

	  


 (Please print or typewrite name and address, 

including postal zip code, of assignee) 
 the
within Note and all rights thereunder, and hereby irrevocably constitutes and appoints 
  

	
	 
	 
	 

 to transfer said Note on the books of the Trustee, with full power of substitution in the premises. 

 

			
	 Dated: ______________________________________________
  

 
 _

	  	 _______________________________ 
NOTICE: The signature to this assignment must correspond with the name as
written upon the face of the within Note in every particular, without alteration or enlargement or any change whatsoever.

		
	_____________________________________________________ 
Signature Guarantee	  	


  
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 EXHIBIT B 

FORM OF 3.150% SENIOR NOTE DUE 2050 

THIS NOTE IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF DTC OR A NOMINEE
OF DTC. THIS NOTE IS EXCHANGEABLE FOR NOTES REGISTERED IN THE NAME OF A PERSON OTHER THAN DTC OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY DTC TO A NOMINEE OF DTC, BY A
NOMINEE OF DTC TO DTC OR ANOTHER NOMINEE OF DTC OR BY DTC OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH A SUCCESSOR DEPOSITARY. 

UNLESS THIS GLOBAL SECURITY IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION
(“DTC”), TO THE ISSUER OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY GLOBAL SECURITY ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF
DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN. 
 BIOGEN INC. 

3.150% Senior Note due 2050 
  

			
	REGISTERED	  	PRINCIPAL AMOUNT
	No. Specimen	  	$[    ]

 CUSIP: [    ] 

ISIN: [    ] 
 Biogen
Inc., a Delaware corporation (herein called the “Company,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., or registered assigns, the
principal sum of $[ ] on May 1, 2050 (the “Maturity Date”) (except to the extent redeemed or repaid prior to the Maturity Date) and to pay interest thereon from April 30, 2020 (the “Original Issue Date”) or from
the most recent Interest Payment Date to which interest has been paid or duly provided for semi-annually at the rate of 3.150% per annum, on May 1 and November 1 (each such date, an “Interest Payment Date”), commencing
November 1, 2020, until the principal hereof is paid or made available for payment. 

  
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 Payment of Interest. The interest so payable, and punctually paid or made available
for payment, on any Interest Payment Date, will, as provided in the Indenture, be paid, in immediately available funds, to the Person in whose name this Note (or one or more Predecessor Securities) is registered at the close of business on
October 15 or April 15 (whether or not a Business Day, as defined in the Indenture), as the case may be, next preceding such Interest Payment Date (the “Regular Record Date”). Any such interest not punctually paid or duly
provided for (“Defaulted Interest”) will forthwith cease to be payable to the Holder on such Regular Record Date, and such Defaulted Interest, may be paid to the Person in whose name this Note (or one or more Predecessor Securities) is
registered at the close of business on a special record date (the “Special Record Date”) for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Notes not less than fifteen days
prior to such Special Record Date, or may be paid at any time in any other lawful manner not inconsistent with requirements of any securities exchange on which the Notes may be listed, and upon such notice as may be required by such exchange, all as
more fully provided in said Indenture. 
 Place of Payment. Payment of principal, premium, if any, and interest on this Note will be
made at the Corporate Trust Office of the Trustee or such other office or agency of the Company as may be designated for such purpose, in such coin or currency of the United States of America as at the time of payment is legal tender for payment of
public and private debts; provided, however, that each installment of interest, premium, if any, and principal on this Note may at the Company’s option be paid in immediately available funds by transfer to an account maintained by
the payee located in the United States. 
 Time of Payment. In any case where any Interest Payment Date, the Maturity Date or any
date fixed for redemption or repayment of the Notes shall not be a Business Day, then (notwithstanding any other provision of the Indenture or this Note), payment of principal or interest, if any, need not be made on such date, but may be made on
the next succeeding Business Day with the same force and effect as if made on such Interest Payment Date, the Maturity Date or the date so fixed for redemption or repayment, and no interest shall accrue in respect of the delay. 

General. This Note is one of a duly authorized issue of Securities of the Company, issued and to be issued in one or more Series under
an indenture, dated as of September 15, 2015 (the “Base Indenture”), between the Company and U.S. Bank National Association (herein called the “Trustee,” which term includes any successor trustee under the Indenture with
respect to a Series of which this Note is a part), as supplemented by a Second Supplemental Indenture thereto, dated as of April 30, 2020 (the “Second Supplemental Indenture” and, together with the Base Indenture, the
“Indenture”). Reference is hereby made to the Indenture for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities, and of the terms upon
which the Securities are, and are to be, authenticated and delivered. This Note is one of a duly authorized Series of Securities designated as “3.150% Senior Notes due 2050” (collectively, the “Notes”), initially limited in
aggregate principal amount to $1,500,000,000. 
 Further Issuance. The Company may from time to time, without the consent of the
Holders of the Notes, issue additional Securities (the “Additional Securities”) of this Series having the same ranking and the same interest rate, maturity and other terms as the Notes. Any Additional Securities of this Series and the
Notes will constitute a single Series under the Indenture and all references to the Notes shall include the Additional Securities unless the context otherwise requires. 

  
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 Events of Default. If an Event of Default with respect to the Notes shall have
occurred and be continuing, the principal of the Notes may be declared due and payable in the manner and with the effect provided in the Indenture. 

Sinking Fund. The Notes are not subject to any sinking fund. 

Optional Redemption. The Notes will be redeemable at any time, at the option of the Company, in whole or from time to time in part,
upon not less than 10 nor more than 60 days’ prior notice, on any date prior to their Maturity at a redemption price, calculated pursuant to the Indenture, which includes accrued interest thereon, if any, to, but not including, the Redemption
Date. In the case of any partial redemption, selection of the Notes for redemption will be made by the Trustee by such methods, as the Trustee in its sole discretion shall deem fair and appropriate. If any Note is to be redeemed in part only, the
notice of redemption relating to such Note shall state the portion of the principal amount thereof to be redeemed. A new Note in principal amount equal to the unredeemed portion thereof will be issued in the name of the Holder thereof upon
cancellation of this Note. 
 Repurchase upon a Change of Control Triggering Event. Upon the occurrence of a Change of Control
Triggering Event with respect to the Notes, the Company shall be required to make an offer to repurchase the Notes on the terms set forth in the Indenture. 

Defeasance and Covenant Defeasance. The Indenture contains provisions for defeasance at any time of (a) the entire indebtedness of
the Company on this Note and (b) certain restrictive covenants and the related Defaults and Events of Default, upon compliance by the Company with certain conditions set forth therein, which provisions apply to this Note. 

Modification and Waivers; Obligations of the Company Absolute. The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each Series. Such amendment may be effected under the Indenture at any time by the Company, and the Trustee with
the consent of the Holders of not less than a majority in aggregate principal amount of the outstanding Notes of each Series affected thereby. The Indenture also contains provisions permitting the Holders of not less than a majority in aggregate
principal amount of the Securities at the time outstanding, on behalf of the Holders of all outstanding Securities, to waive compliance by the Company with certain provisions of the Indenture. Furthermore, provisions in the Indenture permit the
Holders of not less than a majority in aggregate principal amount of the outstanding Securities of individual Series to waive on behalf of all of the Holders of Securities of such individual Series certain past defaults under the Indenture and their
consequences. Any such consent or waiver shall be conclusive and binding upon the Holder of this Note and upon all future Holders of this Note and of any Note issued upon the registration of transfer hereof or in exchange hereof or in lieu hereof,
whether or not notation of such consent or waiver is made upon this Note. 

  
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 No reference herein to the Indenture and no provision of this Note or of the Indenture shall
alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and interest on this Note at the time, place, and rate, and in the coin or currency, herein prescribed. 

Limitation on Suits. As set forth in, and subject to, the provisions of the Indenture, no Holder of any Note will have any right to
institute any proceeding with respect to the Indenture or for any remedy thereunder, unless such Holder shall have previously given to the Trustee written notice of a continuing Event of Default with respect to this Series, the Holders of not less
than 25% in aggregate principal amount of the outstanding Notes shall have made written request, and offered indemnity and/or security, to the Trustee to institute such proceedings as trustee, and the Trustee shall not have received from the Holders
of a majority in principal amount of the outstanding Notes a direction inconsistent with such request and shall have failed to institute such proceeding within 60 days; provided, however, that such limitations do not apply to a suit
instituted by the Holder hereof for the enforcement of payment of the principal of or interest on this Note on or after the respective due dates expressed herein. 

Authorized Denominations. The Notes are issuable only in registered form without coupons in denominations of $2,000 or any integral
multiple of $1,000 in excess thereof. 
 Registration of Transfer or Exchange. As provided in the Indenture and subject to certain
limitations herein and therein set forth, the transfer of this Note is registrable in the register of the Notes maintained by the Registrar upon surrender of this Note for registration of transfer, at the office or agency of the Company in any place
where the principal of and interest on this Note are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Registrar, duly executed by the Holder hereof or his attorney duly
authorized in writing, and thereupon one or more new Notes, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees. 

As provided in the Indenture and subject to certain limitations herein and therein set forth, the Notes are exchangeable for a like aggregate
principal amount of Notes of different authorized denominations, as requested by the Holders surrendering the same. 
 No service charge
shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith. 

Prior to due presentment of this Note for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may
treat the Holder as the owner hereof for all purposes, whether or not this Note be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary. 

Defined Terms. All terms used in this Note, which are defined in the Indenture and are not otherwise defined herein, shall have the
meanings assigned to them in the Indenture. 
 Governing Law. This Note shall be governed by and construed in accordance with the laws
of the State of New York. 

  
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 Unless the certificate of authentication hereon has been executed by the Trustee by manual
signature, this Note shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose. 
 [Remainder of
page intentionally left blank.] 

  
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 IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed and its seal
to be hereunto affixed. 
 Dated: April [    ], 2020 

 

			
	BIOGEN INC.
		
	By:	 	 
		 	Name:
		 	Title:



  
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 TRUSTEE’S CERTIFICATE OF AUTHENTICATION 

This is one of the Notes of the Series designated and referred to in the within-mentioned Indenture, as such is supplemented by the
within-mentioned Second Supplemental Indenture. 
  

			
	U.S. BANK NATIONAL ASSOCIATION, as Trustee
		
	By:	 	 
		 	Name:
		 	Title:


 Dated: April [    ], 2020 

  
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 ASSIGNMENT 

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto 
  

      
  

 
       

 
 PLEASE INSERT SOCIAL SECURITY NUMBER OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE 
  

							
		  	 	  	
		  	 	  	

  
       

 
  

      
  

(Please print or typewrite name and address, 

including postal zip code, of assignee) 
 the
within Note and all rights thereunder, and hereby irrevocably constitutes and appoints 
  

      
  

 
       

 
 to transfer said Note on the books of the Trustee,
with full power of substitution in the premises. 
  

			
	Dated:
                                         
                                         
  	  	  

		  	NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Note in every particular, without alteration or enlargement or any change whatsoever.

  

	
	
	   

	 Signature Guarantee



  
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