X0306 4 2022-03-09 0 0001805890 Fusion Pharmaceuticals Inc. FUSN 0001813574 Valliant John C/O FUSION PHARMACEUTICALS, INC. 2 INTERNATIONAL PLACE, SUITE 2310 BOSTON MA 02110 1 1 0 0 Chief Executive Officer Common Stock 2022-03-09 4 S 0 822 6.94 D 389464 D Common Stock 2022-03-10 4 S 0 1900 7.06 D 387564 D Common Stock 2022-03-11 4 S 0 100 7.13 D 387464 D The sale reported in this Form 4 was effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on December 13, 2021. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $6.82 to $7.08 per share. The reporting person hereby undertakes, upon request of the staff of the U.S. Securities and Exchange Commission, the Issuer or a security holder of the Issuer, to provide full information regarding the number of shares sold at each separate price. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $6.92 to $7.25 per share. The reporting person hereby undertakes, upon request of the staff of the U.S. Securities and Exchange Commission, the Issuer or a security holder of the Issuer, to provide full information regarding the number of shares sold at each separate price. The price reported represents the weighted average sales price of shares sold in multiple transactions at prices ranging from $7.11 to $7.30 per share. The reporting person hereby undertakes, upon request of the staff of the U.S. Securities and Exchange Commission, the Issuer or a security holder of the Issuer, to provide full information regarding the number of shares sold at each separate price. /s/Maria Stahl as Attorney-in-Fact for John Valliant 2022-03-14