Merck agreed to acquire Cidara Therapeutics for about $9.2 billion to secure CD388, a long-acting antiviral designed to prevent seasonal and pandemic influenza. CD388 — a small-molecule neuraminidase inhibitor conjugated to a proprietary Fc fragment — is in the Phase III ANCHOR trial and previously showed strong prevention efficacy in the Phase IIb NAVIGATE study. NAVIGATE topline data reported prevention efficacy (PE) ranging from 57.7% at the 150 mg dose to 76.1% at the 450 mg dose over 24 weeks, and the program has Fast Track and Breakthrough Therapy designations. Merck said the deal aims to bolster its antiviral portfolio ahead of Keytruda patent expirations and to add a potential season‑long prophylactic that could complement vaccines and therapeutics. The acquisition includes Merck’s stated intention to leverage Cidara’s team and manufacturing plans; BARDA had previously agreed to support domestic manufacturing. Investors reacted strongly, sending Cidara’s stock sharply higher on the deal announcement.