144 0001055951 XXXXXXXX LIVE 0002036042 Sionna Therapeutics, Inc. 001-42504 21 HICKORY DRIVE SUITE 500 WALTHAM MA 02451 617-819-2020 OrbiMed Private Investments VIII, LP Shareholder Common Stock TD Cowen

599 Lexington Avenue New York NY 10022

1082480 46330144.00 45150330 05/29/2026 Nasdaq Stock Market Common Stock 02/10/2025 IPO Issuer N 1082480 02/10/2025 Cash N OrbiMed Private Investments VIII, LP

601 Lexington Ave. 54th Floor New York NY 10022

Common Stock 04/14/2026 47814 2128201.14 OrbiMed Private Investments VIII, LP

601 Lexington Ave. 54th Floor New York NY 10022

Common Stock 04/15/2026 235863 10528924.32 OrbiMed Private Investments VIII, LP

601 Lexington Ave. 54th Floor New York NY 10022

Common Stock 04/16/2026 226906 10287918.04 OrbiMed Private Investments VIII, LP

601 Lexington Ave. 54th Floor New York NY 10022

Common Stock 04/17/2026 52397 2341097.96 OrbiMed Private Investments VIII, LP

601 Lexington Ave. 54th Floor New York NY 10022

Common Stock 04/20/2026 2948 131244.96 OrbiMed Private Investments VIII, LP

601 Lexington Ave. 54th Floor New York NY 10022

Common Stock 05/07/2026 48546 2165637.06 OrbiMed Private Investments VIII, LP

601 Lexington Ave. 54th Floor New York NY 10022

Common Stock 05/08/2026 59767 2664412.86 OrbiMed Private Investments VIII, LP

601 Lexington Ave. 54th Floor New York NY 10022

Common Stock 05/11/2026 184639 8534014.58 OrbiMed Private Investments VIII, LP

601 Lexington Ave. 54th Floor New York NY 10022

Common Stock 05/27/2026 101 4493.49 OrbiMed Capital GP VIII LLC is the general partner of OrbiMed Private Investments VIII, LP. OrbiMed Advisors LLC is the managing member of OrbiMed Capital GP VIII LLC. 05/29/2026 02/10/2025 /s/ Douglas Coon, Chief Compliance Officer, OrbiMed Advisors LLC, managing member of the general partner of OrbiMed Private Investments VIII, LP