The U.S. Department of Health and Human Services will cancel contracts and pull funding for some vaccines that are being developed to fight respiratory viruses like COVID-19 and the flu.

Robert F. Kennedy Jr. announced in a statement Tuesday that 22 projects, totalling $500 million US, to develop vaccines using mRNA technology will be halted. 

Kennedy's decision to terminate the projects is the latest in a string that have seen the longtime vaccine critic's agenda overriding scientific criteria at the nation's health department. Kennedy 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. 

The health secretary criticized mRNA vaccines in a video on his social media accounts, explaining the decision to cancel projects being led by the nation's leading pharmaceutical companies, including Pfizer and Moderna, that offer protection against viruses like the flu, COVID-19 and H5N1. 

"To replace the troubled mRNA programs, we're prioritizing the development of safer, broader vaccine strategies, like whole-virus vaccines and novel platforms that don't collapse when viruses mutate," Kennedy said in the video. 

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. 

'Dangerous decision'

"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 the technology offers potential advantages of rapid production, crucial in the event of a new pandemic that requires a new vaccine. 

The shelving of the mRNA projects is short-sighted as concerns about a bird flu pandemic continue to loom, 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. At the White House earlier this year, billionaire tech entrepreneur Larry Ellison praised mRNA for its potential to treat cancer. 

Traditionally, vaccines have required growing pieces of viruses, often in chicken eggs or giant vats of cells, then purifying that material. The mRNA approach starts with a snippet of genetic code that carries instructions for making proteins. Scientists pick the protein to target, inject that blueprint and the body makes just enough to trigger immune protection — producing its own vaccine dose.

In a statement Tuesday, HHS said "other uses of mRNA technology within the department are not impacted by this announcement." 

The abandoned mRNA projects signal a "shift in vaccine development priorities," the health department said in its statement, adding that it will start "investing in better solutions." No details were provided on what those other technologies might be.