KING COUNTY, WASHINGTON — The Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices recommended in September 2025 that children younger than age 4 not receive the combined measles, mumps, rubella, and varicella (MMRV) vaccine. The committee instead recommended that these children receive separate measles, mumps, and rubella (MMR) and varicella vaccines.

This recommendation reverses a 2009 policy where the MMRV vaccine was listed as an option for children under 4 after clinical consultation. In 2009, the committee had recommended co-administered MMR and varicella vaccines as the preferred first-dose option for children younger than age 4 due to an observed increased risk of febrile seizures following the MMRV vaccine.

A study published in JAMA Network Open by Eric Chow, MD, MPH, of Public Health-Seattle & King County, analyzed vaccination data from January 2015 through December 2025 in King County, Washington. The study included 213,445 children aged 12 to 47 months who received one or more doses of measles- or varicella-containing vaccines. Of these children, 14.7% received the MMRV vaccine as their first dose, while 63.8% started with the MMR vaccine co-administered with a separate varicella vaccine. Another 17.8% received the MMR vaccine alone, and 3.7% received the varicella-only vaccine as their first dose.

The study found that children eligible for the federal Vaccines for Children (VFC) program were more likely to receive the MMRV vaccine as their first dose. Hispanic, American Indian or Alaska Native, Black, Native Hawaiian or Pacific Islander, and multiracial children were also more likely to receive the MMRV vaccine as their first dose. Children vaccinated at safety-net clinics in King County were more likely to receive the MMRV vaccine first.

"Combination vaccines, including MMRV, are associated with improved coverage by reducing the number of injections, clinic visits, and costs for families," Chow said. "In safety-net settings, where visit time, vaccine inventory, and follow-up may be constrained, limited access to MMRV could disproportionately affect VFC-eligible children by reducing vaccine options and increasing barriers to timely series completion."

Elizabeth Cope, PhD, MPH, of AcademyHealth, said the result of the ACIP's decision concerning the MMRV vaccine is a contraction of choice. "Combination vaccines' benefits matter most to families with the least slack: hourly work, no paid sick leave, and a follow-up visit that may not happen," Cope said. "The result of ACIP's turn against the MMRV vaccine is a contraction of choice, concentrated among families whose choices were already more constrained by insurance status, clinic access, and follow-up logistics." Cope added that 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. "They are central to evidence-based vaccine policy," she said.