To analyze patterns of measles-containing vaccine (MCV) selection and assess vaccine access and equity implications in King County, Washington.
Approach:
Study Design: Cross-sectional study following STROBE reporting guidelines using data from the Washington State Immunization Information System.
Population: Children born between January 1, 2014, and December 31, 2021, who received 1 or more doses of MCV or varicella-containing vaccines (VCV) between 12 to 47 months of age.
Data Analysis: Data analyzed from October 2025 to May 2026 using R version 4.5, with statistical significance set at P <.05.
Key Findings:
213,445 children received 1 or more MCV or VCV doses; 64% received coadministered MMR + VAR, 18% MMR alone, 15% MMRV, and 4% VAR alone.
Significantly more MMRV-receiving children were from minoritized racial and ethnic groups and were VFC-eligible (P <.001).
95% of children received both MCV and VCV before age 4 years, with disparities in vaccination rates observed.
Interpretation:
Limitations:
Data may be incomplete for vaccines received outside of Washington State.
Results may not be generalizable to non-Universal Purchase states.
