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 on Monday. “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.

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

Speaking in the Oval Office, Trump said that his administration “is recognising gold standard childhood vaccine recommendations for only 11 core vaccinations against the most serious and dangerous diseases”.

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 that 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 Centers for Disease Control and Prevention, external (CDC), there is “no published scientific evidence that shows any benefit in separating the combination MMR vaccine into three individual shots”.

The agency says “most people who get MMR vaccine do not have any serious problems with it”, and that getting the vaccine “is much safer than getting measles, mumps, or rubella”.

Trump’s Secretary of Health and Human Services (HHS) Robert F Kennedy Jr said the proposed changes were meant to give parents choice, not prohibit access to childhood vaccines.

The federal government does not have the authority to implement the new recommendations. Shots that are required for school attendance are set at the state level.