Cidara Therapeutics has announced an expanded and accelerated Phase 3 plan for CD388, its non-vaccine preventative for seasonal influenza, following feedback from the U.S. Food and Drug Administration (FDA). The company says the single Phase 3 trial, if successful, could support a biologics license application (BLA) approval and significantly broaden the population eligible for treatment.

The planned study will now include adults over 65 years of age, in addition to individuals over 12 with high-risk co-morbidities or compromised immune systems. Cidara estimates this expansion could increase the potential U.S. patient population from around 50 million to over 100 million people. The trial will remain global, multicenter, randomized, double-blind and placebo-controlled, assessing the safety and efficacy of a single 450-milligram subcutaneous dose of CD388 administered at the start of the flu season.

Enrollment is targeted to begin by the end of September 2025 in the Northern Hemisphere, continuing into the spring of 2026 in the Southern Hemisphere. The accelerated start moves the trial up by six months from the previous plan, allowing for an interim analysis after the Northern Hemisphere season to review trial assumptions and adjust Southern Hemisphere enrollment as needed. The study aims to enroll 6,000 participants.

Jeffrey Stein, president and chief executive officer of Cidara, said: “The FDA’s input on our Phase 3 study design was invaluable and we welcome the opportunity to expand the trial to include adults over 65 years of age who are among the most vulnerable to serious complications from influenza. Older adults receive less protection from vaccines because the immune system naturally declines with age. Including them in our trial not only addresses a critical unmet need but will also accelerate enrollment. With the success of our financing earlier this summer, we believe that our planned Phase 3 development program will be fully funded through completion, and we look forward to building on the strong Phase 2b NAVIGATE results as we advance CD388 toward becoming a universal, non-vaccine, long-acting option for flu prevention.”

Participants will be randomized 1:1 to receive either CD388 or placebo. The primary endpoint will combine laboratory-confirmed influenza with a body temperature of 37.2°C (99°F) and the presence of either two new or worsening respiratory symptoms, or one respiratory symptom plus one systemic symptom such as headache, fatigue, body aches or feeling feverish.

Cidara’s Phase 3 plan reflects a growing focus on non-vaccine flu prevention and an effort to provide long-acting protection for populations less responsive to traditional vaccines.