3 burning questions about the MMR vaccine, answered

On Friday, former President Donald Trump reaffirmed his stance advocating for modifications to the measles, mumps, and rubella (MMR) vaccine schedule. He suggested that the vaccine be separated into three individual shots, stating, “BREAK UP THE MMR SHOT INTO THREE TOTALLY SEPARATE SHOTS (NOT MIXED!)” on his Truth Social account.

Presently, parents have the option to choose either the MMR vaccine or a combined quadrivalent vaccine that includes measles, mumps, rubella, and varicella (chickenpox) for their children. Medical guidelines suggest administering the combined quadrivalent vaccine may come with a slightly heightened risk of febrile seizures for children under four, leading the Centers for Disease Control and Prevention (CDC) and numerous medical professionals to recommend opting for two separate vaccinations whenever feasible. However, there exists little evidence supporting the notion that further dividing the MMR vaccine and spacing out the injections offers any health advantages. Additionally, this approach could potentially decrease vaccination rates due to the inconvenience of multiple doctor visits.

“There’s no scientific evidence that separating the vaccines provides any medical benefit. I can say that unequivocally,” asserted Jake Scott, an infectious disease physician at Stanford University. “In fact, all of the evidence suggests that the combined vaccine provides equal safety and efficacy, with fewer injections and improved adherence.”

Trump initially broached the topic of separating the MMR vaccine during a press conference on Monday, where he and other officials also discussed a hypothesized correlation between acetaminophen use during pregnancy and rising autism rates. However, experts have stated that the evidence linking autism to Tylenol is lacking, and the American College of Obstetrics and Gynecology has recognized the safety and benefits of acetaminophen during pregnancy.

Friday’s remarks from Trump suggest a departure from vaccine policies that have yet to be publicly entertained by his own administration’s vaccine advisers. Earlier this month, a committee from the CDC voted to recommend that children under four receive the varicella vaccine as a separate shot—a recommendation already available on the CDC’s website—yet did not consider separating the MMR vaccine into three individual shots.

Trump has not provided any new data indicating that the combined MMR vaccine poses risks that haven’t already been evaluated by healthcare professionals or advisory panels. While it remains unclear where Trump derived the notion of separating the shots, it has been notably championed by Andrew Wakefield, a controversial British anti-vaccine advocate. Wakefield published a now-retracted 1998 paper suggesting a link between MMR vaccines and autism, which led to his expulsion from the British medical register.

In the aftermath of Trump’s initial comments, Wakefield expressed his support via social media, asserting that the former president was endorsing “Wakefield recommendations” regarding vaccine separation and calling for significant reform of the childhood vaccination schedule.

“I haven’t heard anyone make that claim in years, actually, since Andrew Wakefield did that years ago,” remarked William Moss, director of the International Vaccine Access Center at Johns Hopkins University. “So I’m genuinely shocked that Trump would suggest that. The bottom line is that there’s absolutely no valid reasoning behind separating those vaccines, and monovalent vaccines aren’t even available in the United States.” He further stated that while Trump’s remarks are cause for concern, the President cannot unilaterally alter vaccine policy.

Is it possible to get separate measles, mumps, and rubella vaccines?

No, monovalent vaccines for measles, mumps, and rubella were phased out in the U.S. in 2009 due to the success of the combined vaccine. Currently, the FDA has three MMR vaccines available, all of which are combinations.

Reintroducing monovalent vaccines would likely be a protracted process, taking years to undergo a detailed review, new clinical trials, and FDA approval, according to Scott.

What are the risks associated with the MMR vaccine?

Hundreds of millions of MMR vaccine doses have been administered globally. The vaccine is extremely effective in preventing disease, with research indicating that the side effects are minimal. There exists a small heightened risk of febrile seizures in young children within 12 days of receiving the MMR vaccine, calculated at about one additional seizure per 3,000-4,000 vaccinations.

While receiving the MMRV vaccine may slightly increase the risk of febrile seizures, the CDC’s Advisory Committee on Immunization Practices (ACIP) continues to endorse the standard two-shot regimen, allowing for parent choice regarding the MMRV shot when appropriate for their child’s health. The CDC clarifies that “febrile seizures can be alarming, but nearly all children recover quickly, and there are no long-term effects or permanent harm.”

What could happen if monovalent vaccines become more common?

Experts are concerned that separating the MMR vaccine could lead to decreased vaccination rates, placing an additional burden on parents and pediatricians. One study indicated that 69% of children who received a combination vaccine completed the vaccination series compared to just 50% who opted for single antigen vaccines.

“Regardless of the underlying intent, the outcome is entirely predictable: decreased vaccination rates, increased disease incidence, and ultimately, more children succumbing to preventable illnesses,” said Scott. “The only practical effect of proposing to separate vaccines that cannot realistically be separated is to sow doubt about the existing vaccination schedule among parents.”

Trump’s rhetoric comes on the heels of the most significant measles outbreak in years in the U.S. Research has demonstrated that particularly low vaccination rates contributed to outbreaks in counties like Gaines County, Texas. “These situations highlight the ongoing struggle to maintain community immunity amid vaccine hesitancy and disruptions to routine vaccination programs that have led to drops in MMR coverage,” the research concluded.

This advocacy for monovalent vaccines represents a contradictory stance for the administration, particularly given Health Secretary Robert F. Kennedy Jr.’s critiques of the number of vaccines children receive—an issue that would be exacerbated with the introduction of monovalent options.

Experts consulted by STAT reiterated that the combined vaccine has been available for over 50 years, contributing to the eradication of measles and rubella in the U.S. during the early 2000s.

“Since then, we’ve risked the reintroduction of diseases like measles, which is highly contagious, due to some parents withholding vaccinations for their children,” noted William Schaffner, an epidemiologist and public policy professor at Vanderbilt University.