That kind of shot was first used during the Covid-19 pandemic, but the health secretary has been sharply critical of the technology.

Health Secretary Robert F. Kennedy Jr. announced plans Tuesday to cancel $500 million in vaccine development projects. In a statement from his office, the longtime vaccine critic said all projects to be halted use mRNA technology.

The US Department of Health and Human Services (HHS) plans to cancel $500m (£376m) in funding for mRNA vaccines being developed to counter viruses like the flu and Covid-19. The move will impact 22 projects being led by major pharmaceutical companies, including Pfizer and Moderna, for vaccines against bird flu and other viruses, HHS said.