X0306 4/A 2021-10-01 2021-10-04 0 0001653087 Alector, Inc. ALEC 0001635264 King Robert C/O ALECTOR, INC. 131 OYSTER POINT BLVD, SUITE 600 SOUTH SAN FRANCISCO CA 94080 0 1 0 0 Chief Development Officer Common Stock 2021-10-01 4 A 0 5939 0.00 A 528256 D The shares are represented by restricted stock units which vest in 12 equal quarterly installments beginning on December 1, 2021. This amendment on Form 4 is filed to adjust an overstatement of 2,028 shares of Common Stock in Columns 4 and 5 of Table I in a Form 4 filed on October 4, 2021. /s/ David Oh, by power of attorney 2021-10-08