X0306 4 2017-12-20 0 0001178670 ALNYLAM PHARMACEUTICALS, INC. ALNY 0001458494 Vaishnaw Akshay 300 THIRD STREET CAMBRIDGE MA 02139 0 1 0 0 EVP, R&D Common Stock 2017-12-19 5 G 0 E 320 0 D 11215 D Common Stock 338 I by Managed Account Performance Based Stock Option 2016 (right to buy) 42.22 2017-12-20 4 A 0 6250 0 A 2017-12-20 2026-12-20 Common Stock 6250 6250 D The reporting person owns 338 shares of ALNY common stock under the ALNY 401(k) plan as a result of the ALNY 401(k) matching contribution program. On December 20, 2016, the reporting person was granted a performance based stock option to purchase shares of ALNY common stock. One quarter of the shares subject to the option will vest upon the achievement of each of four specific clinical development, regulatory or commercial events, as approved by our compensation committee. Effective December 20, 2017, the compensation committee of the Company determined the first performance criterion had been met and the option vested as to one-quarter of the shares. /s/ Michael P. Mason, Attorney-in-Fact for Akshay K. Vaishnaw 2017-12-21