WASHINGTON — President Donald Trump signed an executive order that would recommend breaking up the combined measles, mumps and rubella vaccine into three separate shots and unilaterally overhauling the national childhood vaccination recommendations.

The order signed Monday also calls for childhood immunizations to be given at separate medical visits and proposes three separate categories for childhood vaccinations, according to a fact sheet viewed by Bloomberg.

Trump during a signing ceremony at the White House connected the issue to rates of autism in U.S. children. Scientific evidence has shown no link between autism and childhood vaccines, and decades of research have failed to identify a singular cause of autism.

“There’s a reason for such epidemic rates of autism, and we’re going to bring it back to much closer to where it was,” the president said. “While we do not know exactly what the cause is with respect to autism, it is essential to our research efforts that we have the very best vaccine recommendations in the entire world.”

If implemented, the changes would mean parents would have to make many more trips to the doctor to get the same protection against diseases for their young kids. That raises the risk that some would miss immunizations at a time when vaccination coverage is already eroding, and put more children in danger of becoming infected with a disease that can be prevented by the shots.

The order amounts to one of Trump’s most sweeping efforts yet to pare down the number of shots recommended for children. The president turned his attention to the issue as he struggles to bring an end to the war in Iran and grapples with a shaky economy, all of which have put his fellow Republicans in danger of losing control of Congress in the November midterm elections.

The order puts a spotlight on a topic officials had previously sought to downplay ahead of the midterms. An internal memo earlier this year advised health officials to focus on less divisive subjects like food guidelines and healthcare costs, as polling showed broad support for routine childhood vaccines in competitive election districts.

Despite the scientific consensus, some anti-vaccine activists believe that the MMR shot causes autism in kids, and by separating the shots, researchers would know which vaccine purportedly leads to development of the neurological disorder.

A May executive order sought to align U.S. shot schedules with countries that recommend fewer immunizations. A court has blocked other attempts by officials including Health and Human Services Secretary Robert F. Kennedy Jr. to alter official vaccine schedules and remake the advisory committee that oversees them.

Under the new order, children are recommended to receive protection for 11 diseases — down from 18. It also directs states that use school requirements to consider updating its laws based on the new recommendations.

Bloomberg News previously reported the Trump administration was considering an executive order on vaccines and autism, despite no scientific evidence suggesting a link.

The MMR is a two-dose combination shot that helps reduce the number of immunizations given to children. No vaccine is entirely perfect, but the MMR is one of the most effective shots on the market. It’s 97% effective in preventing a measles infection after two doses, according to the U.S. Centers for Disease Control and Prevention.

Splitting the shot could be expensive and complicated for MMR manufacturers Merck & Co. and GSK Plc. There is no evidence that there is any benefit to separating the combination shot, according to the Infectious Disease Society of America.

Last year, Trump called for breaking up the shot into three separate vaccines. Then-acting director of the CDC Jim O’Neill called on drugmakers to “develop safe monovalent vaccines to replace the combined MMR,” in a social media post.

Japan stopped using the combination shot in 1993, leading to a huge spike in measles cases and more than 500 pediatric deaths about a decade later. The country only recently approved a triple combination MMR shot manufactured by Daiichi Sankyo, the first approval in 30 years.

Last year, a key U.S. vaccine advisory committee voted against Merck’s combination MMR and chickenpox shot in the youngest children due to an elevated risk of febrile seizures. About 15% of children under 4 take the shot.

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