efitazanamivir alfa

efitazanamivir alfa (CD388 / MK-1406) is an investigational, long-acting drug-Fc conjugate (DFC) designed for the universal prevention of seasonal and pandemic influenza A and B. Developed originally by Cidara Therapeutics (which was acquired by Merck & Co. in late 2025) and previously in collaboration with Janssen, efitazanamivir alfa consists of multiple copies of the small molecule neuraminidase inhibitor zanamivir stably conjugated to an engineered human IgG1 Fc fragment via a PEG-based linker. The Fc fragment is engineered to extend the drug's half-life, enabling season-long protection with a single subcutaneous or intramuscular dose. Unlike traditional vaccines, efitazanamivir alfa directly inhibits viral replication by blocking neuraminidase and does not rely on mounting an immune response, making it potentially highly effective in immunocompromised individuals, older adults, and other high-risk populations. It is currently in Phase 3 clinical development (e.g., the ANCHOR trial) for influenza prevention.