Cidara shares double after drug succeeds in flu prevention study

Cidara Therapeutics shares surged as much as 102% Monday after the biotech announced that its experimental influenza prevention candidate CD388 hit all primary and secondary endpoints in a Phase IIb trial.

The long-acting antiviral, administered as a single injection at the beginning of the flu season, is a drug-Fc conjugate (DFC) that links copies of a potent neuraminidase inhibitor to a proprietary Fc fragment. Cidara says DFCs differ from vaccines and monoclonal antibodies in that they are low molecular weight biologics engineered to function like long-acting small-molecule inhibitors.

CD388 was designed to provide universal protection against seasonal and pandemic influenza strains, and "because [it] is not a vaccine, its activity is not reliant on an immune response and thereby is expected to be efficacious in individuals regardless of immune status," the company added.

The NAVIGATE trial randomised about 5000 healthy unvaccinated adults across sites in the US and UK who are not at risk of complications from flu. Participants received single doses of CD388 (150 mg, 300 mg or 450 mg) or placebo. The primary endpoint measured laboratory-confirmed influenza infections over 24 weeks. Results showed prevention efficacy of 57.7%, 61.3% and 76.1% for the three dose groups, respectively, with all reaching statistical significance compared to placebo.

"Best case" scenario

RBC Capital Markets analyst Brian Abrahams said the results represent a "best case" scenario for Cidara. "The magnitude of protective efficacy looks impressive, with all doses clearing our ~50% protective efficacy bar and the highest dose exceeding our best case scenario of 65%+ in protective efficacy."

Meanwhile, secondary endpoints examining different fever thresholds (≥37.8°C and ≥37.2°C) also achieved statistical significance, with CD388 maintaining protective efficacy for up to 28 weeks.

No drug-related serious adverse events were reported, and treatment-emergent side effects showed no dose-dependent trends between the CD388 and placebo groups. Injection-site reactions occurred at similar rates across all CD388 doses and placebo.

"These Phase IIb results support the potential of CD388 to be a highly effective and well-tolerated seasonal prophylactic for high-risk individuals, such as those with compromised immune systems or those at a heightened risk of severe illness due to underlying health conditions," stated Nicole Davarpanah, Cidara's chief medical officer. The firm has submitted an end-of-Phase II meeting request to the FDA to discuss Phase III trial design and timing.

The results come as the US Centers for Disease Control and Prevention's recently reconstituted vaccine advisory committee prepares to meet this week. Earlier this month, Health and Human Services Secretary Robert F. Kennedy Jr. abruptly fired all 17 members of the Advisory Committee on Immunization Practices (ACIP) and changed the upcoming meeting agenda. The revised schedule now includes new presentations on thimerosal-containing flu vaccines and measles vaccines.