On Monday, Acting CDC Director Jim O’Neill urged vaccine manufacturers to develop separate vaccines for measles, mumps, and rubella instead of continuing with the current combination vaccine known as the MMR vaccine. In a post on X, O'Neill advocated for the creation of “safe monovalent vaccines,” which target one virus at a time, rather than the combined approach used today.
O'Neill's statement echoed a recent comment made by former President Donald Trump, who suggested on Truth Social that individuals should consider breaking up the MMR vaccine into three separate shots. However, it is important to note that, as of now, no monovalent vaccines for measles, mumps, or rubella have been approved in the United States. The Centers for Disease Control and Prevention (CDC) has also stated that there is no published scientific evidence supporting the benefits of separating the combined vaccine.
While O'Neill's call for change raises questions about the feasibility and likelihood of developing separate vaccines, a spokesperson for the Department of Health and Human Services, Andrew Nixon, mentioned that standalone vaccinations could potentially reduce the risk of side effects and provide parents with more choices regarding childhood immunizations. However, he did not provide evidence to support his claims about side effects.
The MMR vaccine has been administered as a combination shot since 1971, primarily to minimize the number of injections children receive. The current vaccination schedule recommends that children receive the two-dose MMR vaccine, with the first dose given between 12 and 15 months and the second dose between 4 and 6 years of age. If the MMR vaccine were to be separated, children would need to receive a total of six injections instead of two, significantly increasing the burden of vaccination.
While at a White House event on September 22, Trump expressed his preference for individual over combined shots. He raised concerns about the number of vaccines children receive, stating, “too many different things are going into that baby at too big a number.” Trump further asserted that the MMR vaccine should be administered separately, claiming, “there’s no downside in taking them separately.”
Merck, the pharmaceutical company responsible for manufacturing the MMR vaccine since its inception, responded to O'Neill's call by stating that using individual vaccines could lead to an increased number of injections, potentially resulting in delayed or missed immunizations. Merck also indicated that evidence suggests the use of combination vaccines enhances childhood vaccination outcomes, increasing both the completion and compliance rates of immunizations.
This year, the United States has recorded the highest number of measles cases since 2000, the year the country eliminated the disease. Health Secretary Robert F. Kennedy Jr., known for his past anti-vaccine activism, has made numerous false claims regarding measles vaccines. Despite his controversial stance, Kennedy has acknowledged the importance of getting vaccinated.
The Department of Health and Human Services has already acted to limit access to the combination MMR and chickenpox vaccine for children under 4. On September 18, the CDC’s vaccine advisory committee advised against the combined vaccine for this age group, a recommendation that O’Neill, who also serves as the deputy health secretary, endorsed. Most pediatricians typically administer the chickenpox vaccine and the MMR vaccine separately for young children.
The committee's recommendation was based on an observed increased risk of febrile seizures—seizures triggered by fevers that generally resolve quickly. While combination MMR and chickenpox vaccines can still be administered to older children, there is currently no evidence indicating an increased risk of febrile seizures in that age group. Trump later expressed his approval that chickenpox vaccines would be given separately from MMR vaccines.
