GENEVA — The World Health Organization has defended the evidence-based process used to establish childhood immunisation schedules, warning against changes that are not supported by scientific evidence after U.S. President Donald Trump ordered a reduction in the number of routinely recommended childhood vaccinations.
Trump signed an executive order on Monday calling for a U.S. childhood vaccination schedule covering 11 immunisations. He said the change would provide children with “gold-standard” protection and bring U.S. practice closer to that of other developed countries.
WHO spokesperson Tarik Jašarević said on Tuesday that vaccine recommendations were based on more than 60 years of research involving WHO, national health authorities and independent expert groups. The timing of vaccines is determined after scientific assessments of when people are most vulnerable to particular diseases and how the immune system develops, he said.
“What comes out from WHO is science-based,” Jašarević told reporters at a briefing in Geneva. “We hope that all countries will use this best scientific evidence that we have.”
WHO guidance is intended to help countries develop vaccination programmes suited to their own circumstances. The organization’s current recommendations cover routine immunisation for children, adolescents and adults and include guidance on the timing and intervals of primary and booster doses. WHO says national schedules also take account of local disease risks, health systems and other country-specific factors.
Vaccine experts have said countries cannot necessarily be compared simply by counting the number of vaccines on their schedules because disease risks, healthcare systems and immunisation policies differ.
Trump’s order also calls for the combined measles, mumps and rubella vaccine to be separated into individual shots. Vaccine maker Merck has said there is no published scientific evidence showing a benefit from splitting the combined vaccine and has warned that requiring additional visits could increase the likelihood of delayed or missed vaccinations.
Medical associations and public health experts have also criticized the proposed changes, saying the existing U.S. schedule reflects decades of evidence and the health needs of the U.S. population. Physicians have warned that reducing routine recommendations could leave some children more vulnerable to vaccine-preventable diseases and create uncertainty for parents.
The American Academy of Pediatrics has separately maintained its 2026 immunisation schedule, which recommends protection against 18 serious diseases. The academy says its recommendations are based on reviews of vaccine safety, disease epidemiology, vaccine effectiveness and potential complications of the diseases.
WHO’s recommendations remain the international reference framework for countries developing routine immunisation programmes, while national authorities retain responsibility for setting schedules according to local conditions.
