Objective:

To characterize the populations that selected the combination measles, mumps, rubella, and varicella vaccine (MMRV) as their first measles-containing vaccine and to inform interpretations of recent US vaccine policy changes.

Approach:

• Study Design: Cross-sectional analysis of the Washington State Immunization Information System, including 213,445 children from King County, Washington, born between 2014 and 2021.
• Data Evaluation: Evaluated the first measles-containing or varicella-containing vaccine administered and examined demographic characteristics, geographic distribution, clinic type, and Vaccines for Children (VFC) program eligibility.

Key Findings:

• 64% of children received MMR + VAR as their first vaccination, 18% received MMR alone, 15% received MMRV, and 4% received VAR alone.
• MMRV use remained stable throughout the study period.
• Children receiving MMRV were more likely to be eligible for the VFC program and receive care at safety-net clinics.
• 95% of children completed both measles-containing and varicella-containing vaccine recommendations before age 4 years.
• Children receiving MMRV were more likely to identify as Hispanic, American Indian or Alaska Native, Black, Native Hawaiian or Pacific Islander, multiracial, or another or an unspecified race, and reside in southern King County.

Interpretation:

The study provides insights into access to MMRV among different populations, particularly in relation to VFC eligibility and safety-net clinics.

Limitations:

• Vaccine records may have been incomplete for children vaccinated outside Washington State.
• Findings from a single county may not be generalizable to other jurisdictions.
• The study did not evaluate the effects of the September 2025 policy change.

Conclusion:

The study suggests that access to recommended vaccines may be impacted by policy changes.

Sources:

• JAMA Network Open