X0306 4 2021-02-12 0000875045 BIOGEN INC. BIIB 0001672709 Vounatsos Michel BIOGEN INC. 225 BINNEY ST. CAMBRIDGE MA 02142 1 1 Chief Executive Officer Common Stock 2021-02-12 4 F 0 7248 278.03 D 43905.286 D Common Stock 2021-02-12 4 M 0 5693 0 A 49598.286 D Common Stock 2021-02-12 4 M 0 5259 0 A 54857.286 D Common Stock 2021-02-12 4 M 0 5337 0 A 60194.286 D Common Stock 2021-02-12 4 F 0 2525 278.03 D 57669.286 D Common Stock 2021-02-12 4 F 0 2333 278.03 D 55336.286 D Common Stock 2021-02-12 4 F 0 2367 278.03 D 52969.286 D Restricted Stock Unit 0 2021-02-12 4 M 0 5693 0 D 2021-02-12 Common Stock 5693 6419 D Restricted Stock Unit 0 2021-02-12 4 J 0 6419 0 D 2021-02-12 Common Stock 6419 0 D Restricted Stock Unit 0 2021-02-12 4 M 0 5259 0 D 2022-02-12 Common Stock 5259 19789 D Restricted Stock Unit 0 2021-02-12 4 J 0 7263 0 D 2022-02-12 Common Stock 7263 12526 D Restricted Stock Unit 0 2021-02-12 4 M 0 5337 0 D 2023-02-12 Common Stock 5337 32343 D Restricted Stock Unit 0 2021-02-12 4 J 0 7221 0 D 2023-02-12 Common Stock 7221 25122 D Represents shares withheld to satisfy the withholding tax liability due upon the vesting of shares, as previously disclosed by reporting person on January 29, 2021. The number of RSUs reported represents the maximum possible number of shares that are eligible for vesting, which is 200% of the number of shares at target payout. One-third of these RSUs are eligible to vest on each of the first three anniversaries of the grant date. The actual number of shares that will vest on each vesting date will be determined by comparing the price of Biogen common stock on such vesting date to the price on the grant date (i.e., number of vested shares = number of shares at target payout times [the 30-day average closing stock price ending on the vesting date divided by the 30-day average closing stock price following and including the grant date]). This represents the difference between the maximum possible number of shares that were eligible for vesting and the actual number that vested. /s/ Suzanne Murray, Attorney in Fact for Michel Vounatsos 2021-02-17