X0306 4 2022-06-16 0 0001653087 Alector, Inc. ALEC 0001214127 LAVIGNE LOUIS J JR C/O ALECTOR, INC. 131 OYSTER POINT BLVD, SUITE 600 SOUTH SAN FRANCISCO CA 94080 1 0 0 0 Common Stock 2022-06-16 4 A 0 9459 0.00 A 9459 D Common Stock 10552 I See footnote Stock Option (right to buy) 8.07 2022-06-16 4 A 0 18918 0.00 A 2032-06-16 Common Stock 18918 18918 D The reported shares are represented by restricted stock units, or RSUs, which vest on the earlier of (i) June 16, 2023 or (ii) the date of the Issuer's next annual meeting of stockholders. The shares held of record by Lavrite, LLC, for which the reporting person serves as managing director. The shares subject to the option vest in 12 equal monthly installments beginning on July 16, 2022, or if earlier, the date of the Issuer's next annual meeting of stockholders. /s/ Calvin Yu, by power of attorney 2022-06-21