New Influenza Vaccine Provides Long-Lasting Protection and Higher Efficacy

A new clinical trial shows a single shot of a long-lasting influenza (flu) drug may protect people for an entire season, and it might do so more effectively than vaccines.

The study, which took place in the United States and the United Kingdom, enrolled 5,000 healthy adults, none of whom had received the influenza vaccine prior to the study. Enrollees were given one of three different doses of the vaccine, called CD388 (manufactured by Cidara), or a placebo vaccine under the skin between September and December 2024. Over the next 24 weeks, the researchers tallied the number of participants who had respiratory symptoms, such as coughing and a fever, and a confirmed test for the influenza virus. The highest dose of the drug provided 76.1 percent protection from disease, compared with a placebo vaccine. According to Nicole Davarpanah, Cidara’s chief medical officer, all three doses of the vaccine provided “highly statistically significant protection,” although the lowest had only 57.7 perfect efficacy and the middle dose 61.3 percent. No serious side effects occurred at any dose.

The CD388 vaccine contains a reformulated version of zanamivir, a flu drug also known as Relenza that GSK brought to market in 1999 and is approved to both treat and prevent disease. Zanamivir, which must be inhaled daily, targets neuraminidase, an enzyme made by the virus that frees newly made virions from the surface of infected cells. To create a longer-lasting version, Cidara developed a chemical variant of the drug and attached several copies of it to a piece of an antibody called the Fc fragment, which is engineered to resist being broken down by the human body.

“This is one of the most exciting recent advances for influenza prevention,” says Kathleen Neuzil, a veteran influenza vaccine researcher recently forced out of her job as head of the Fogarty International Center at the National Institutes of Health by President Donald Trump’s administration. The drug’s promise echoes that of the anti-HIV drug lenacapavir, which protects people from infection for six months and last week won approval from the U.S. Food and Drug Administration as a so-called pre-exposure prophylactic.

Seasonal influenza vaccines, which are given either by injection or as a nasal spray, are designed to protect against at least three of the seasonal strains that circulate each winter. Their effectiveness at preventing disease depends heavily on how well they match the flu strains going around in the human population, but average only about 40 percent because mutations in flu viruses often allow them to dodge immune responses. In contrast, CD388 is effective against a wide variety of strains. The drug attacks a region of neuraminidase that cannot easily change without compromising viral fitness.