President Donald Trump’s latest executive order calls for the measles, mumps, rubella (MMR) vaccine to be administered in three doses, but doctors and other experts say the initiative lacks scientific basis and is unlikely to get off the ground.
President Trump said Monday, without providing evidence, that the combination version of the vaccine could be “pretty deadly,” even though the vaccines have repeatedly been shown to be safe and effective in large studies. Experts called the claim “completely false” and said there is no scientific data to show the benefits of separating the shots.
Splitting the vaccine also comes with “significant logistical limitations,” and three single doses that require multiple doctor visits could further delay or miss immunizations in children, Neil Mania, a professor of public health at Northeastern University, told CNBC.
“They’re not solving problems here; they’re creating new problems,” Mania said. “Based on faulty science and political ideology, they are trying to turn something that works into something we don’t know what will happen.”
Dr. Andrew Racine, president of the American Academy of Pediatrics, told reporters Wednesday that the U.S. is already seeing a decline in the percentage of parents willing to use the MMR vaccine to immunize their children, contributing to the recent resurgence in measles cases in the United States. The number of measles cases in the United States this year is the highest in decades.
William Moss, a pediatrician and professor of epidemiology at Johns Hopkins University, said President Trump’s comments and recommendations could further erode public confidence in the safety of the MMR vaccine.
About 9% of parents reported skipping or postponing MMR vaccination for their children, according to a 2025 survey conducted by the health policy organization KFF and the Washington Post. It is unclear how this will compare to last year.
It’s also not clear where President Trump first got the idea to split the shot, but some experts say the idea likely goes back to British gastroenterologist Andrew Wakefield. He is an anti-vaccine advocate and published a paper in 1998 claiming a link between the MMR vaccine and an increase in autism. The paper was later retracted and Mr Wakefield was removed from the UK medical register.
Why splitting of MMR vaccines does not occur
U.S. President Donald Trump holds up a “Gold Standard Pediatric Vaccine Recommended” sign during the signing of an executive order in the Oval Office of the White House on Monday, August 10, 2026 in Washington, DC, USA.
Bonnie Cash | Bloomberg | Getty Images
Manufacturer of MMR vaccine – Merck and GSK – There appears to be little incentive to develop a standalone vaccine, as doing so would take considerable time and resources away from other important work towards treating other diseases and finding cures. These vaccines are likely to reach the market long after President Trump’s term ends.
“I don’t think there is anywhere else in the world where a vaccine manufacturer would be interested in developing a monovalent measles, mumps, rubella vaccine and going through a rigorous regulatory process to get FDA approval and clinical trials,” Moss said. “That would be a stupid investment.”
AAP’s Racine also said it would likely take more than a decade to develop these single shots.
Merck added in a statement Wednesday that there is evidence to suggest that the use of combination vaccinations improves childhood vaccination outcomes and increases rates of completion and compliance with all recommended doses.
Currently, one dose of the MMR vaccine is given at 12 to 15 months of age, and a second dose is given at 4 to 6 years of age. Separating the vaccine could mean that children need to receive six different doses at a young age.
“It’s so counterintuitive and counterproductive,” Moss said. It is ironic that they argue that children are receiving too many shots, and then instead propose policies that would only increase the number of shots that children receive. ”
Northeastern’s Mania said even one visit can already be difficult for parents who have to take time off from work. Access to health care is also more complex in certain communities, such as rural areas, he added.
Mania said the U.S. childhood immunization schedule is designed based on both a child’s “immune system readiness” for a particular immunization and their risk for a particular disease. Spacing out these vaccines may increase the likelihood that children will miss or delay vaccination against at-risk preventable diseases.
Racine added: “Why aren’t we giving our children vaccines that are safe and prevent death?”
He also noted that two healthy children died from measles in the United States last year.
Some experts worry that the splitting of MMR shots and President Trump’s broader efforts to change federal vaccine recommendations could confuse parents and cause more parents to refrain from vaccinating their children. Some states may also follow the new guidelines.
Moss said he does not expect this effort to have an immediate or short-term impact on the ongoing measles outbreak.
Still, Maniar stressed that “we should do everything possible to increase vaccination rates, rather than implementing policies that create further barriers to vaccination.”
