The US Department of Health and Human Services (HHS) plans to cancel $500m (£376m) in funding for mRNA vaccines being developed to counter viruses that cause diseases such as the flu and Covid-19.
That will impact 22 projects being led by major pharmaceutical companies, including Pfizer and Moderna, for vaccines against bird flu and other viruses, HHS said.
Health Secretary Robert F Kennedy Jr, a vaccine sceptic, announced he was pulling the funding over claims that "mRNA technology poses more risks than benefits for these respiratory viruses".
Doctors and health experts have criticised Kennedy's longstanding questioning of the safety and efficacy of vaccines and his views on health policies.