Single antiviral shot could offer better protection than flu vaccines
A long-lasting formulation of an antiviral drug greatly reduced people’s risk of a symptomatic flu infection in a trial, and should even be effective against new strains
By Carissa Wong
30 June 2025
Influenza virus particles viewed with an electron microscope, with added colour
John G/Imago/Alamy
A single dose of a long-lasting antiviral drug has shown promise in protecting against all flu strains, raising hopes that it could protect those who are most vulnerable.
The flu kills thousands of people every year and the rapid evolution of new variants could trigger the next pandemic. Each year, scientists update flu vaccines to match the strains of influenza virus they expect to circulate most widely during the upcoming flu season. These vaccines prompt the immune system to produce antibodies that stop the virus from entering your cells.
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Scientists are working towards a universal flu vaccine that would protect against all strains that infect people, but such a vaccine would still have limitations.
“Even if someone came up with the first [approved] universal flu vaccine, it is never going to protect everyone, because people have various degrees of immune response to vaccines,” says Jeffrey Stein, CEO at biotech company Cidara. For instance, vaccines are generally less effective in older people or those with suppressed immune systems.
To address this, Stein and his colleagues developed a treatment called CD388, which contains zanamivir, an antiviral drug that is approved for treating infections caused by all flu strains that infect people. Zanamivir is usually cleared from the body within hours, but the team chemically modified it to linger for months in the body, where it can rapidly destroy invading flu viruses. “It doesn’t engage the immune system,” says Stein.
