President Donald Trump on Monday signed an executive order calling for a reduction in childhood vaccinations against diseases from 18 immunisations recommended by the Centres for Disease Control and Prevention in 2024 to 11.

Mr Trump also called for the combined mumps, measles and rubella (MMR) vaccine to be split into three single-disease shots during separate visits to the hospital.

“Effective immediately, my administration is recognising gold-standard childhood vaccine recommendations for only 11 core vaccinations against the most serious and dangerous diseases, along with the MMR, which hopefully will be split up,” Mr Trump said during a signing ceremony at the White House.

The president, who has long doubted the safety of MMR vaccines over alleged links with autism, repeatedly cited the prevalence of the neurodevelopmental condition. However, studies have not found any established links between the vaccine and autism.

He argued that the MMR shots could be “quite lethal” if given at once.

Asked by a reporter for evidence to support his claims that it could be lethal, he said, “What I’ve heard is that there are some people that say it is that way. Decades ago, children received only a small fraction of the vaccines required today.

“In those times, people were much healthier, and of course the high rates of autism now observed did not exist. There are some groups that have virtually no problem with autism. They’re groups that aren’t big into the world of vaccines. So, there is something wrong.”

Under the order, the recommended childhood immunisations include polio, human papillomavirus, measles, mumps, rubella, pneumococcal disease, diphtheria, tetanus, pertussis, Haemophilus influenzae type B, and chickenpox.

“We’re reducing them,” Mr Trump noted. “It’s not only that you’re doing fewer vaccines, or jabs, as they say, but you’re doing them in a series of visits to the doctor.”

The president’s order called on states with school vaccine requirements to consider his “gold standard” recommendations and update their laws. It also advised federal agencies to advance the recommendations to ensure “Americans have the best scientific information.”

Meanwhile, the CDC said the MMR vaccine “has been linked with a very small risk of febrile seizures”. However, it said seizures after the vaccination are “rare and are not associated with any long-term effects”.

“Getting MMR vaccine is much safer than getting measles, mumps, or rubella,” it said.

It advised people who have had life-threatening reactions to the antibiotic neomycin, or any MMR vaccine component, against getting the vaccine.

Health secretary Robert F Kennedy Jr, who had long opposed vaccination over alleged links with autism, claimed Mr Trump’s order sought to give parents choice and not to limit access to vaccines.