US President Donald Trump has signed an order that calls for fewer childhood vaccines and also recommends splitting the mumps, measles and rubella (MMR) shots

"Decades ago, children received only a small fraction of the vaccines required today," Trump said. "In those times, people were much healthier and of course the high rates of autism now observed did not exist"

The president has long cast doubt on the safety of MMR vaccines, but multiple studies have found no connection between the shots and autism

Medical experts have criticised the new order and said it could reduce vaccination rates and expose children to harmful diseases

The order also recommends that the number of childhood vaccines drop to 11 from the existing 18 recommended by the American Academy of Pediatrics (AAP)

Trump's order serves as guidance, not a mandate, since shots required for school attendance are set at the state level, rather than by the federal government

The immunisations recommended for all children under the order are for measles, mumps, rubella, diphtheria, tetanus, pertussis, polio, Haemophilus influenzae type B, pneumococcal disease, human papillomavirus, and varicella or chicken pox

"We're reducing them," Trump said. "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 suggested the MMR vaccine could be "quite lethal" if given at once. He compared it to pouring a bottle of soda into a child's body. According to the FDA, a single dose of MMR is 0.5ml

When a reporter asked for evidence of the "lethal" claim, Trump said: "What I've heard is that there are some people that say it is that way"