Merck agreed to buy Cidara Therapeutics for about $9.2 billion to acquire CD‑388, a late‑stage, long‑acting antiviral being developed as a season‑long prophylactic against influenza. The deal, announced this week, pays roughly $221.50 per Cidara share and folds an asset with phase III studies and prior BARDA support into Merck’s infectious‑disease push. CD‑388 combines a potent small‑molecule neuraminidase inhibitor with an antibody Fc fragment and showed strong phase IIb protection signals across A and B strains. Merck framed the acquisition as part of a strategy to replenish growth ahead of anticipated Keytruda patent expiration, adding a potentially first‑in‑class preventive option for high‑risk populations. The transaction accelerates Merck’s timing to market by internalizing late‑stage development and commercial scale‑up for a prophylactic that could compete with, or complement, seasonal vaccination strategies.