X0306 4 2022-02-12 0000875045 BIOGEN INC. BIIB 0001263839 ALEXANDER SUSAN H BIOGEN INC. 225 BINNEY STREET CAMBRIDGE MA 02142 1 EVP Chief Legal Off & Corp Sec Common Stock 2022-02-12 4 M 0 1154 0 A 45032 D Common Stock 2022-02-12 4 F 0 512 214.59 D 44520 D Common Stock 2022-02-12 4 M 0 1126 0 A 45646 D Common Stock 2022-02-12 4 F 0 500 214.59 D 45146 D Common Stock 2022-02-12 4 F 0 1044 214.59 D 44102 D Restricted Stock Unit 0 2022-02-12 4 M 0 1154 0 D 2022-02-12 Common Stock 1154 2190 D Restricted Stock Unit 0 2022-02-12 4 J 0 2190 0 D 2022-02-12 Common Stock 2190 0 D Restricted Stock Unit 0 2022-02-12 4 M 0 1126 0 D 2023-02-12 Common Stock 1126 5308 D Restricted Stock Unit 0 2022-02-12 4 J 0 2090 0 D 2023-02-12 Common Stock 2090 3218 D Represents shares withheld to satisfy the withholding tax liability due upon vesting of shares, as previously disclosed by reporting person on January 21, 2022. 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/ Wendell Taylor, attorney-in-fact for Susan Alexander 2022-02-15