US President Donald Trump's administration has announced it would terminate 22 federal contracts for mRNA-based vaccines, questioning the safety of a technology credited with helping end the Covid pandemic and saving millions of lives.
The announcement was made by Health Secretary Robert F Kennedy Jr.
"We reviewed the science, listened to the experts, and acted," Kennedy said in a statement.
The health department's Biomedical Advanced Research and Development Authority (BARDA) is "terminating 22 mRNA vaccine development investments because the data show these vaccines fail to protect effectively against upper respiratory infections like COVID and flu," he added.
"We're shifting that funding toward safer, broader vaccine platforms that remain effective even as viruses mutate."
The changes affect Moderna's mRNA bird flu vaccine - a move the company itself disclosed in May - as well as numerous other programmes, including "rejection or cancellation of multiple pre-award solicitations" from pharmaceutical giants Pfizer and Sanofi.
In total, the affected projects are worth "nearly $500 million," the Department of Health and Human Services (HHS) said. Certain late-stage projects were excluded from the move "to preserve prior taxpayer investment."
"Let me be absolutely clear: HHS supports safe, effective vaccines for every American who wants them," Mr Kennedy said.
"That's why we're moving beyond the limitations of mRNA and investing in better solutions."
Mr Kennedy has long questioned the safety of vaccines, contrary to scientific evidence, and he has also suggested a link between vaccines and autism.
Since taking office as Secretary of Health and Human Services, Mr Kennedy has overseen a major overhaul of US health policy - firing, for example, a panel of vaccine experts that advise the government and replacing them with his own appointees.
In its first meeting, the new panel promptly voted to ban a longstanding vaccine preservative targeted by the anti-vaccine movement, despite its strong safety record.
Unlike traditional vaccines, which often use weakened or inactivated forms of the target virus or bacteria, mRNA shots deliver genetic instructions into the host's cells, prompting them to produce a harmless decoy of the pathogen and train the immune system to fight the real thing.
Though in development for decades, mRNA vaccines were propelled from lab benches to widespread use through President Trump's Operation Warp Speed - a public-private partnership led by BARDA that poured billions into companies to accelerate development.
The technology's pioneers, Katalin Kariko and Drew Weissman, were awarded the 2023 Nobel Prize in Medicine for their work contributing "to the unprecedented rate of vaccine development during one of the greatest threats to human health in modern times."
Late last month, federal data showed that vaccination rates for several diseases, including measles, diphtheria and polio decreased among US pre-schoolers in the 2024-25 school year from the year before.
The US Centers for Disease Control and Prevention released the new figures at a time when the US faces a growing measles outbreak, with confirmed cases this month reaching the highest level since the disease was declared eliminated from the country in 2000.
The CDC data show vaccination rates have steadily trended down since the Covid-19 pandemic. For the measles, mumps and rubella vaccine, coverage went from 95.2% in the 2019-2020 school year to 92.7% last year, before landing at 92.5% in 2024-2025.
In Texas, the epicentre of the recent measles outbreak, MMR coverage has fallen to 93.2% from 96.9% in 2019.
Most people are protected from measles through herd immunity when more than 95% of people in the community are vaccinated, the CDC website says.
An HHS spokesperson said the data released on 31 July showed a "majority" of children continue to get routine childhood immunisations, and that vaccination remains the most effective way to protect children from measles and whooping cough.
"The decision to vaccinate is a personal one," the spokesperson said. "Parents should consult their health care providers on options for their families."
In addition, exemptions from one or more vaccines increased to 3.6% in 2024-2025 from 3.3% the year before, the CDC website said. Exemptions, which can be granted on medical or religious grounds, increased in 36 states and DC, with 17 states reporting exemptions exceeding 5%, it said.
