Merck (known as MSD outside the US and Canada) has entered into a definitive agreement to acquire Cidara Therapeutics, a biotech company developing drug-Fc conjugate (DFC) therapeutics, including CD388, its investigational candidate for flu prevention.
CD388 is an investigational DFC comprising multiple copies of a potent small-molecule neuraminidase inhibitor stably conjugated to a proprietary Fc fragment of a human antibody. Unlike a vaccine, CD388’s mechanism of action does not rely on eliciting an immune response and is therefore expected to be effective regardless of an individual’s immune status.
“We continue to execute our science-led business development strategy, augmenting our pipeline with CD388, a potentially first-in-class, long-acting antiviral designed to prevent influenza in individuals at higher risk of complications,” said Robert M Davis, Chairman and CEO, Merck. “We intend to build on the Cidara team’s remarkable progress and are confident that CD388 has the potential to be another important driver of growth through the next decade, creating real value for shareholders.”
CD388 previously received Breakthrough Therapy Designation and Fast Track Designation from the US Food and Drug Administration (FDA) following the phase 2b NAVIGATE study, which met all primary and secondary endpoints related to preventing symptomatic, laboratory-confirmed influenza in healthy, unvaccinated adults aged 18-64.
The candidate is currently under evaluation for flu prevention in the randomised, double-blind, placebo-controlled phase 3 ANCHOR study, which is assessing its efficacy and safety in adults and adolescents at higher risk of influenza-related complications. The first participants were dosed in September 2025, with an interim analysis anticipated in early 2026.
“This milestone represents a transformational moment for Cidara and for our mission to redefine influenza prevention,” said Jeffrey Stein, President and CEO of Cidara. “The phase 2b NAVIGATE study delivered compelling results that demonstrate CD388’s potential to provide an additional option to vaccines and antivirals to help address unmet needs in influenza prevention. Merck’s global development, regulatory and commercial capabilities provide the expertise and resources needed to bring this important innovation to those individuals who need it most.”
Under the terms of the agreement, Merck, through a subsidiary and subject to customary closing conditions, will acquire all outstanding shares of Cidara at $221.50 per share, valuing the transaction at approximately $9.2bn. Completion is expected in the first quarter of 2026.