Children receiving a combination measles, mumps, rubella, and varicella vaccine (MMRV) may be more likely to come from low-income and underserved communities, according to a new study published in JAMA Network Open. 

The findings come less than a year after a Centers for Disease Control and Prevention Advisory Committee on Immunization Practices (ACIP) vote to remove the MMRV vaccine as a recommended option for children under the age of four years. The vote also excluded it from coverage by Vaccines for Children (VFC), a federal program that provides vaccines to kids whose parents may not be able to afford them.

The vaccine covers not only measles and mumps, but “German measles” (rubella) and chickenpox (varicella), as well.

Combination vaccines may help improve coverage

The study examined how more than 213,000 children in King County, Washington, received their first measles- and varicella-containing vaccines from 2015 to 2025. Researchers, primarily from Public Health–Seattle & King County, found that children who received the MMRV vaccine were more likely to get care at safety-net clinics, belong to racial and ethnic minority groups, and qualify for enrollment in VFC. 

Of the children in the study, 15% received the MMRV vaccine as their first dose and 64% received separate measles, mumps, and rubella (MMR) and varicella vaccines (VAR) during the same visit. Although those receiving the MMRV vaccine were in the minority, they were more likely to be Hispanic; American Indian or Alaska Native, Black, Native Hawaiian or Pacific Islander, or multiracial; eligible for VFC; vaccinated in safety-net clinics; and receiving catch-up vaccinations after the recommended age.

This population might be at risk of not receiving recommended vaccines if options become limited.

Combination vaccines reduce the number of injections, clinic visits, and costs required to complete a vaccine series, note the authors, and in clinics serving families with limited resources, that may help improve vaccine coverage. “This population might be at risk of not receiving recommended vaccines if options become limited,” the researchers write. In an accompanying commentary, Elizabeth Cope, PhD, MPH, and Aaron Carroll, MD, agree: “Those benefits matter most to families with the least slack: hourly work, no paid sick leave, and a follow-up visit that may not happen.” 

ACIP recommendation made without equity considerations 

When ACIP opted to remove the MMRV vaccine as a recommended option for young children in September 2025, the vote occurred without a population analysis, notes the commentary. 

“It also came without an Evidence-to-Recommendations framework analysis,” or the “structured process ACIP has historically used to document how equity, feasibility, acceptability, patient values, and resource implications factor into any recommendation change,” Cope and Carroll write. 

Transparency in the sense of public visibility remained intact; transparency in the sense of auditable, evidence-based deliberation did not.

Those weren’t the only procedural concerns. “Liaison organizations were excluded from deliberations,” continues the commentary, and the “MMRV vote itself required reconsideration after confusion among committee members about what had been voted on. Transparency in the sense of public visibility remained intact; transparency in the sense of auditable, evidence-based deliberation did not.”

In 2009, faced with MMRV safety data indicating a small but real increase in febrile seizure risk for children under age four, an earlier iteration of ACIP—before it was stacked with vaccine skeptics last year—voted to make receiving separate MMR and VAR vaccines during the same visit the default recommendation, but allowed for MMRV vaccination after provider-caregiver consultations. “That kind of compromise is what the patient-clinician conversation is for,” notes the commentary. 

Seizure risk is genuine

The study comes with caveats. It was limited to a single county, so the findings may not apply nationwide. And the risk of febrile seizure is genuine.

 “We are not arguing about the size of that risk,” write Copeland and Carroll. “We are arguing about the procedure that should have weighed the risks and about the stakeholders, including families, who were not in the room when it was weighed.”

For Copeland and Carroll, the findings highlight broader issues around how vaccine policy decisions are made. “Questions about who uses an intervention, who benefits from having a choice, and who is affected by reduced access are not peripheral to vaccine policy,” Cope and Carroll wrote. “They are central to evidence-based vaccine policy.”