The World Health Organisation has publicly rebuked Donald Trump's efforts to overhaul US childhood vaccination policy, warning that his approach contradicts decades of scientific evidence. Trump signed an order on Monday calling for a review of school vaccine mandates and renewing calls to split the combined measles, mumps and rubella (MMR) jab into three separate shots, an idea long championed by Health Secretary Robert F. Kennedy Jr, who founded an anti-vaccine group and has repeatedly promoted a disproven link between MMR and autism. The dispute matters because it comes as the US battles its worst measles outbreak in 35 years, with children about to return to school, raising fears infections could spread further.

WHO director general Tedros Adhanom Ghebreyesus said the science is "unequivocal" that vaccines, including MMR, are safe and do not cause autism, and insisted policy should be guided by rigorous, independent, transparent review rather than political influence. He warned that delaying or separating vaccine doses unnecessarily does not improve safety and can leave children unprotected. Kennedy has already launched a review of long-used vaccines, revised the child vaccination schedule and cut funding for new vaccine development, moves condemned by medical and scientific bodies and partly blocked earlier this year by US courts; Trump withdrew the US from the WHO on his first day back in office in 2025.