The Potential Ramifications of Changing the MMR Vaccine Into 3 Separate Immunizations

Earlier this week, President Trump signed an executive order changing the pediatric vaccine schedule, and in many ways and reflecting the wishes of the current Advisory Committee on Immunization Practices (ACIP) and the Health and Human Services Secretary Robert F Kennedy for decreased access to immunizations. The order changes the spacing of immunizations, breaks the existing measles, mumps, and rubella (MMR) vaccine into 3 separate vaccines, and continuing to push the “shared clinical-decision making” category for numerous vaccines that were previously recommended.

The MMR vaccine change is one of the most unusual parts of the executive order as it has not been something previously discussed in terms of breaking it into 3 single-antigen vaccines. The efficacy and safety for the vaccine are well-established, so the move is baffling.  

Sharon Nachman, chief of pediatric infectious diseases at Stony Brook Children's Hospital, points out the vaccines were originally given as individual shots but there were issues of compliance and young children could be susceptible to these preventable diseases.

“We moved away from single, monovalent vaccines to combine them because we wanted to actually protect children and cut down on those diseases, and essentially that's exactly what happened when the vaccine became combined,” she said.

Another aspect that is hard to understand for an ACIP and administration that wants to see less vaccines, is making the MMR vaccine into 3 separate ones, and therefore making full immunization compliance increase from 2 shots to 6 overall.

Nachman says if they are given as individual shots, incidence rates for each of these diseases will increase.

“That's exactly what will happen if you spread out the shots, and make them monovalent instead of a trivalent [vaccine]. You will expect measles cases to increase because you're actually delaying the vaccination for those,” Nachman said. “As a reminder, for a live vaccine, you must wait a month between doses. So the earliest you could get protection would be starting at 12 to 15 months—one dose, wait a month; another dose, wait a month; a third dose, wait the third month. And then 2 years later, the same scenario would apply. So that really puts the American public, particularly children, at risk because there'll be longer times before they are fully vaccinated.”

And this is happening during a time when this year’s measles cases alone are exceptionally high. The Johns Hopkins University measles tracker counted 2295 cases as of July 22, edging past the 2289 cases reported for the full year of 2025 and marking the highest annual total since measles was declared eliminated in the country in 2000.¹ And this is with 5 months of the calendar year left and kids going back to school.

The individual vaccines for mumps, measles, and rubella are no longer manufactured in the US, so that would take considerable time and new studies to validate the new vaccines.

“You're actually going to have to study it all over again and compare it to the single-dose multi-viral vaccine. That's going to take 5 years at a minimum. You're going to have to enroll 60,000-80,000 children at least,” Nachman said. “That means you have to find families that agree that by chance alone they will get 6 shots vs 2 shots, and see what happens when exposed to disease…those diseases, except for measles, have really been eliminated in the United States. So that means you can't show efficacy because…we have to wait until those diseases come back and then show that the vaccine is as efficacious given as single shots compared to giving it as 2-combined vaccine doses.”

This is the first episode of 2-part series. In the second episode, Nachman discusses the administration’s shared clinical-decision making category for vaccines, and what the order does in terms of vaccine guidance overall.

Reference
1.Vision Monday Staff. Measles cases set 35-year US record with months to go in 2026. VisionMonday. Published July 22, 2026. Accessed July 23, 2026. https://www.visionmonday.com/eyecare/health-watch/article/measles-cases-set-35year-us-record-with-months-to-go-in-2026