Cidara Therapeutics’ investigational long-acting antiviral, CD388, has achieved statistically significant protection against influenza in a Phase 2b trial, paving the way for further regulatory engagement with the FDA.

The randomised, double-blind, placebo-controlled study assessed CD388 across three dose levels in healthy adults. All three treatment arms met the primary endpoint, demonstrating statistically significant protection against symptomatic influenza infection compared to placebo. Cidara says the antiviral was also generally well tolerated, with no new safety signals reported.

Unlike conventional influenza vaccines, CD388 is a drug-Fc conjugate administered once per season, designed to offer passive protection regardless of circulating strains. The investigational prophylactic forms part of Cidara’s Cloudbreak platform, which applies targeted immunotherapeutic approaches to infectious diseases and oncology.

Jeffrey Stein, president and CEO of Cidara, said the results are a significant milestone, supporting the first potential alternative to the seasonal influenza vaccine. He added that the data show the therapy could protect individuals at high risk of influenza complications who may not mount an adequate immune response to vaccines.

The Phase 2b data come from a natural exposure challenge trial, evaluating incidence of symptomatic flu illness in participants over a full flu season. Following these results, the company has requested an end-of-Phase 2 meeting with the FDA, expected in Q3 2025, to discuss advancing to pivotal studies.

Flu continues to cause significant morbidity and mortality globally, with existing vaccine uptake and efficacy varying by season and population. A long-acting, strain-agnostic antiviral could prove an important addition to the armamentarium, particularly for immunocompromised individuals or the elderly.

Cidara previously partnered with Janssen (a Johnson & Johnson company) on CD388, though Janssen terminated the collaboration in 2023 amid broader pipeline cuts. Cidara has since retained full rights to the programme.

The company also has other Cloudbreak candidates in development, targeting respiratory syncytial virus (RSV) and oncology indications.