Acting CDC director calls for MMR vaccine to be broken up into three shots

Jim O’Neill, who is serving as the acting director of the Centers for Disease Control and Prevention, has called for major changes to the vaccine for measles, mumps, and rubella (MMR), proposals that lack support from scientific evidence. His comments have heightened criticism from the Trump administration regarding a vaccine that plays a critical role in the childhood vaccination schedule.

“I urge vaccine manufacturers to create safe monovalent vaccines instead of the combined MMR vaccine and propose to separate the MMR vaccine into three distinct shots,” O’Neill stated in a post on X on Monday. His post did not specify reasons for breaking up the MMR shot but referenced a message from President Trump that advocated for administering the vaccines at separate medical appointments.

Experts have previously warned that this proposal could make children more susceptible to infections and may not be feasible, as separate vaccines for these diseases are currently unavailable in the U.S.

A study published in 2017 revealed that 69% of U.S. children receiving the combination vaccine completed the full vaccination series, compared to only 50% of those whose parents chose single antigen vaccines.

O’Neill also serves as the deputy secretary of Health and Human Services, and his comments reflect ongoing scrutiny of childhood vaccines from the current administration. Recently, President Trump suggested splitting the MMR vaccine into three separate doses to be administered at different doctor’s visits, adding to a series of unfounded concerns about vaccines raised by the president at a White House event.

The CDC’s Advisory Committee on Immunization Practices voted to limit access to the MMRV vaccine, which combines the MMR vaccine with one for varicella (chickenpox), recommending it only for children aged four and older. Younger children should receive the MMR and varicella vaccines separately, as was already standard practice.

Scientific evidence does not support that administering the MMR vaccine in separate doses provides any safety or effectiveness benefits. The notion stems from Andrew Wakefield, who falsely claimed a link between the MMR vaccine and increased autism rates. Wakefield’s misleading paper has since been retracted, and he has been removed from the U.K.’s medical register. Numerous studies have confirmed that no connection exists between the MMR vaccine and autism.

The development of monovalent vaccines could take several years. This process would involve lengthy reviews, new clinical trials, reorienting vaccine development processes, and seeking FDA approval.

The measles, mumps, and rubella vaccine has been in use for over 50 years, administered to millions without significant issues.

The vaccine is highly effective in preventing disease, with minimal risks of side effects.

There is a small increased risk of febrile seizures occurring in children within 12 days after receiving the MMR vaccine, estimated by a CDC scientist at one additional seizure for every 3,000-4,000 MMR vaccinations. The MMRV vaccine increases these odds for younger children, which is why the CDC advises administering the varicella vaccine separately for infants.

Even if the administration does not proceed with introducing monovalent vaccines, rhetoric from high-ranking officials could dissuade parents from vaccinating their children in the future.

“Regardless of their intentions, the predictable result will be lower vaccination rates, increased disease prevalence, and more children suffering from preventable illnesses,” stated Jake Scott, an infectious disease physician at Stanford University, as reported by STAT. “Proposing to split vaccines that are not separable will only lead parents to question the current vaccination schedule.”