Acting CDC director, citing Trump directive, calls for MMR shot to be split into three despite no evidence of benefit

By Meg Tirrell, CNN

(CNN) — The acting director of the US Centers for Disease Control and Prevention called for vaccine makers to develop separate shots against measles, mumps and rubella to replace combination MMR vaccines, despite no evidence of any benefit to getting the shots separately.

“I call on vaccine manufacturers to develop safe monovalent vaccines to replace the combined MMR and ‘break up the MMR shot into three total separate shots’,” Jim O’Neill, who also serves as deputy secretary of the US Department of Health and Human Services, wrote in a post on X on Monday. He quoted from a September 26 post by President Donald Trump.

The president didn’t give a reason when he called for breaking up the vaccine, which has been approved as a combination in the US since 1971. The CDC says on its website that “no published scientific evidence shows any benefit in separating the combination MMR vaccine into three individual shots.”

Andrew Nixon, HHS’s director of communications, told CNN that “standalone vaccinations can potentially reduce the risk of side effects and can maximize parental choice in childhood immunizations,” although he did not provide evidence that breaking up the MMR shot specifically would reduce any risk of side effects. The CDC notes that side effects from combination vaccines “are usually mild” and “similar to those of the individual vaccines given separately.”

Separating the MMR vaccine into three shots would “not make that vaccine safer,” said Dr. Paul Offit, a vaccine scientist at Children’s Hospital of Philadelphia and former member of the CDC’s independent vaccine advisory group. “It would just make it more expensive and less likely to be used.”

Merck, which makes one of two approved MMR vaccines in the US, told CNN that it had prioritized making the combination over components protecting against one disease at a time “to meet the public health and medical need for vaccination against measles, mumps and rubella.”

“Use of the individual components of combination vaccines increases the number of injections for the individual and may result in delayed or missed immunizations,” a spokesperson for Merck said in a statement. The company also pointed out that “there are no approved US monovalent measles, mumps and rubella single antigen vaccines.”

GSK, the maker of the other MMR vaccine approved for use in the US, said in a statement, “Combination vaccines play a crucial role in improving vaccination coverage rates; their safety and efficacy have been demonstrated by decades of research. By reducing the number of separate injections required, combination vaccines allow for a simpler and more efficient immunization process, which is essential for timely protection against disease.”

The idea of splitting up the MMR vaccine isn’t new, but it has been thoroughly studied, Offit said. There were calls to do so after a now-retracted 1998 paper from former British physician Andrew Wakefield suggested a link between the combination MMR vaccine and autism, he said.

“Before the claim was discredited, researchers took it seriously, investigated it thoroughly, and found no link,” the American Academy of Pediatrics says on its website. “This research, in many countries, involving thousands of individuals, has spanned multiple decades.”

Trump first brought up the idea of splitting the MMR vaccine during his news conference on autism last month, which was primarily focused on Tylenol, despite no evidence that the pain reliever and fever reducer causes autism.

“The MMR, I think, should be taken separately. This is based on what I feel,” Trump said at the time.

“It seems to be that when you mix them, there could be a problem,” the president continued, without identifying what that problem might be. “So there’s no downside in taking them separately. In fact, they think it’s better, so let it be separate.”

Trump also referenced the fact that the chickenpox, or varicella, vaccine is offered as a combination with MMR, and the CDC’s outside group of vaccine advisers recently voted that children should receive their first doses of MMR and varicella separately.

The MMRV vaccines are given as two doses, the first around age 1 and the second around 4 to 6. There is a small but increased risk of febrile seizure when the MMRV combination is given as the first dose, so the CDC had already recommended that the varicella vaccine be given separately for children under 4. It left the option, though, for parents and physicians to decide what worked best for them.

The advisers’ vote changed that, saying the chickenpox vaccine should be given separately for the first dose. Febrile seizures, while frightening, haven’t been associated with any long-term health effects, the CDC says, and there’s no increased risk for the combination MMRV vaccine in children ages 4 to 6.

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