October 09, 2025
2 min read
Cidara announced Thursday that it received a breakthrough therapy designation from the FDA for an investigational long-acting drug to prevent seasonal influenza.
The drug, called CD388, has been designed to protect patients from both seasonal and pandemic influenza viruses with a single injection, although it is not a vaccine.
The FDA granted breakthrough therapy designation to Cidara’s investigational non-vaccine influenza preventive.
Thursday’s announcement came a week after Cidara said it had secured up to $339 million from the Biomedical Advanced Research and Development Authority — better known as BARDA — to support development and manufacturing of the drug, and more than 2 years after CD388 was granted fast-track status by the FDA.
In a press release, Cidara president and CEO Jeffrey Stein, PhD, said the FDA designations “[underscore] the importance of CD388 as a potential new non-vaccine prophylactic for seasonal influenza.”
For years, scientists have pursued influenza vaccines that can provide long-lasting protection against changing seasonal influenza viruses and also protect against pandemic flu viruses. Research into so-called universal influenza vaccines usually involves targeting areas of the virus that are less likely to mutate than the hemagglutinin surface protein targeted by current vaccines.
CD388 is not a vaccine or a monoclonal antibody, and it does not rely on an immune response to protect the recipient against influenza, according to Cidara. Instead, it is a type of therapy called a drug-Fc conjugate, which are “designed to function as long-acting small molecule inhibitors,” according to the company.
Cidara said the breakthrough therapy designation was based on positive results from the randomized, double-blind, placebo-controlled phase 2b NAVIGATE trial. According to topline results from the trial that were publicized by Cidara in June, CD388 was between 58% and 76% protective against seasonal influenza over the course of 6 months among adults aged 18 to 64 years, depending on the dose.
The breakthrough therapy designation will allow Cidara to work with the FDA to accelerate the development of CD388 for a potential approval down the line. The designation applies to adolescents and adults “at higher risk of influenza complications due to underlying immunodeficiency, are at higher risk of severe influenza despite influenza vaccination, or those for whom vaccines are contraindicated,” according to Cidara.
“Individuals who have chronic medical conditions, advanced age, or are immune compromised may not be adequately protected by current vaccines, leaving them at higher risk for infection and complications from flu,” Stein said in the release. “As a long-acting prophylactic drug, CD388’s activity does not rely on an immune response, making it a potential prevention option for high-risk individuals as well as those for whom vaccines are contraindicated.”
Perspective
The efficacy of influenza vaccines has always been suboptimal, leaving vaccinated people still at risk for infection and sometimes severe bouts of influenza.
CD388 represents an innovative approach to prevention, coupling an antiviral drug to an antibody fragment, extending the half-life of the molecule to provide durable protection.
As this is an antiviral medication, it will work universally to protect against all strains of influenza (unlike the vaccine, which is dependent on an adequate match).
Amesh A. Adalja, MD
Senior Scholar, Johns Hopkins Center for Health Security
Disclosures: Adalja reports no relevant financial disclosures.
