Study reveals disparities in MMRV vaccine use among low-income and minority families
A new study in King County shows that the MMRV vaccine, which carries a slightly higher risk of febrile seizures, is disproportionately given to vulnerable groups, including low-income and minority toddlers.
In 2009, the Advisory Committee on Immunization Practices (ACIP) of the U.S. Centers for Disease Control and Prevention reviewed data and concluded that the MMR+V vaccine (separate shots for measles, mumps, rubella, and varicella) is preferred over MMRV (a single combined shot) as the first dose for toddlers aged 12 to 15 months. The reason: a slightly increased risk of febrile seizures with MMRV — 7 to 8.5 cases per 10,000 first doses, compared with 3.2 to 4.2 per 10,000 with MMR+V. Although febrile seizures are generally harmless and children typically recover fully, ACIP recommended MMR+V as the preferred option. MMRV remained available as an alternative with parental consultation.
New research covering data from 2015 to 2025 in King County found that MMRV use held steady at 15% over the decade. However, children receiving MMRV as their first dose were more likely to be from racial or ethnic minorities, to receive the vaccine later (between 16 and 47 months rather than 12–15 months), and to be eligible for a federal program providing free vaccines to low-income families. They were also nearly four times more likely to be vaccinated at a safety-net clinic.
The findings highlight systemic inequities: vulnerable populations are more likely to receive the less recommended vaccine. Although the risk difference is small, it disproportionately affects those already at higher risk.
