Trump wants to split the MMR vaccine. Experts say that's unlikely — and comes with consequences

President Donald Trump's latest executive order calls for splitting the measles, mumps and rubella, or MMR, vaccine into three separate shots – but doctors and other experts say that effort has no scientific basis and is unlikely to get off the ground.

Trump on Monday said without evidence that the vaccine could be "quite lethal" in its combined form, even though the shot has repeatedly been proven safe and effective across large-scale studies. Experts called that claim "completely false" and said there is no scientific data showing benefits of separating the shot.

Splitting the vaccine would also come with "significant logistical limitations," and having three standalone shots that require multiple doctor's visits could result in more delayed or missed vaccinations among kids, Neil Maniar, a public health professor at Northeastern University, told CNBC.

"They're not solving a problem here. They're creating a new one," Maniar said. "Based on false scientific rationale and political ideology, they're changing something that works into something that we have no idea what it will do."

The U.S. has already seen a decrease in the share of parents who are willing to use the MMR shot to vaccinate their children, which has contributed to the recent resurgence in U.S. measles cases, Dr. Andrew Racine, president of the American Academy of Pediatrics, told reporters on Wednesday. The U.S. has logged its highest number of measles cases in decades this year.

Trump's rhetoric and recommendations could also further undermine the public's confidence in the safety of the MMR vaccine, said William Moss, a pediatrician and epidemiological professor at Johns Hopkins University.

Roughly 9% of parents report either skipping or delaying the MMR vaccine for their children, according to a 2025 survey conducted by health policy organization KFF and the Washington Post. It's unclear how that compares to previous years.

It's also not clear where Trump initially got the idea to split the shots, but some experts say it can likely be traced to a British gastroenterologist, Andrew Wakefield. He is an anti-vaccine advocate who published a paper in 1998 claiming to show a connection between MMR vaccines and an increase in autism. That paper has since been retracted, and Wakefield was removed from the U.K.'s medical register.

Manufacturers of the MMR vaccine – Merck and GSK – seem to have little incentive to develop standalone shots, which would take significant time and resources away from their other crucial work toward treating and finding cures to other diseases. Those vaccines would likely reach the market long after Trump's term ends.

"I don't see any world in which vaccine manufacturers have any interest in developing and going through the rigorous regulatory process, getting FDA approval, doing the trials for monovalent measles, mumps, and rubella vaccines," said Moss. "It would be a foolish investment to make."

AAP's Racine also said that it would likely take more than a decade to develop those standalone shots.

In a statement on Wednesday, Merck added that evidence suggests using combination shots improves childhood vaccination outcomes, increasing the completion of all recommended doses and compliance rates.