Research Summary

County-Level Trends Reveal Declining MMR Vaccination Coverage Across the US Post-Pandemic

Anthony Calabro, MA

Key Highlights

  • Mean measles-mumps-rubella (MMR) vaccination rates declined from 93.9% pre-pandemic to 91.3% post-pandemic across 2066 US counties.
  • 78% of counties with available data reported decreased vaccination coverage.
  • Only four states showed increased county-level MMR vaccination rates: California, Connecticut, Maine, and New York.

In a recent research letter published in JAMA, investigators from Johns Hopkins University (Baltimore, MD), detailed their county-level analysis of measles-mumps-rubella (MMR) vaccination trends among US children from 2017 to 2024. Their analysis showed a national decline in vaccine coverage, particularly after the COVID-19 pandemic.

Among 2066 counties across 33 states with both pre- and post-pandemic data, the mean two-dose MMR vaccination rate dropped from 93.92% to 91.26%, a mean decline of 2.67%. The analysis showed that 78% of these counties experienced a decrease in coverage during the study period.

While national- and state-level declines in childhood MMR vaccination are well documented, localized trends are less understood. The current study addressed that gap by assembling a high-resolution, standardized dataset that captured spatiotemporal variability in vaccine coverage. Given the sharp rise in US measles cases—1001 confirmed cases across 31 jurisdictions as of May 14, 2025—these findings offer insights into regional vulnerabilities and potential hotspots for vaccine-preventable disease resurgence.

Researchers collected publicly available two-dose MMR vaccination data from state health departments for the 2017-2018 through 2023-2024 school years, focusing primarily on kindergartners. Where exact measures were unavailable, comparable proxies were used. The final dataset includes at least 1 year of county-level vaccination rates from 2237 counties in 38 states, with a subset of 2066 counties in 33 states having both pre- and post-pandemic data. Analyses were performed using Python.

The county-level analysis highlighted stark heterogeneity in vaccination coverage within and between states. For example, only four of 33 states showed a post-pandemic increase in county-level vaccination rates: California, Connecticut, Maine, and New York. The drop in coverage, the authors noted, raises concern about increased measles susceptibility within the United States.

This study is limited by inconsistencies in data availability and reporting across states, which affected the completeness and comparability of the dataset. Some student populations, such as homeschooled children or those in non-reporting schools, may be underrepresented.

“Our county-level dataset complements the state- and national-level CDC data, confirming a widespread decline in MMR vaccination rates in the US after the COVID-19 pandemic while revealing significant heterogeneity in vaccination patterns within and across states,” the authors concluded.

Reference
Dong E, Saiyed S, Nearchou A, Okura Y, Gardner LM. Trends in county-level MMR vaccination coverage in children in the United States. JAMA. Published online June 2, 2025. doi:10.1001/jama.2025.8952.