The US Department of Health and Human Services will cancel contracts and pull funding for some vaccines being developed to fight respiratory viruses such as Covid-19 and the flu.

US Secretary of Health and Human Services Robert F. Kennedy Jr announced on Tuesday (local time) that 22 projects, totalling $US500 million ($A772 million), to develop vaccines using mRNA technology will be halted.

Kennedy’s decision to terminate the projects is the latest in a string of decisions that have put the long-time vaccine critic’s doubts about shots into full effect at the nation’s health department.

He has pulled back recommendations around the Covid-19 shots, fired the panel that makes vaccine recommendations, and refused to offer a vigorous endorsement of vaccinations as a measles outbreak worsened.

Kennedy criticised mRNA vaccines in a video on his social media accounts, explaining the decision to cancel projects being led by leading US pharmaceutical companies, including Pfizer and Moderna, that offer protection against viruses such as the flu, Covid-19 and H5N1.

“To replace the troubled mRNA programs, we’re prioritising the development of safer, broader vaccine strategies, like whole-virus vaccines and novel platforms that don’t collapse when viruses mutate,” he said.

Infectious disease experts say the mRNA technology used in vaccines is safe, and they credit its development during the first Trump administration with slowing the 2020 coronavirus pandemic. Future pandemics, they warned, will be harder to stop without the help of mRNA.

“I don’t think I’ve seen a more dangerous decision in public health in my 50 years in the business,” said Mike Osterholm, a University of Minnesota expert on infectious diseases and pandemic preparations.

He noted mRNA technology offered potential advantages of rapid production, crucial in the event of a new pandemic that required a new vaccine.

The shelving of the mRNA projects was short-sighted as concerns about a bird flu pandemic continued, said Dr Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia.

“It’s certainly saved millions of lives,” Offit said of the existing mRNA vaccines.

Scientists are using mRNA for more than infectious disease vaccines, with researchers around the world exploring its use for cancer immunotherapies.

-AAP