County vaccination data may mask school-level measles risk
Pockets of low vaccination rates in some schools help explain why measles outbreaks have been climbing in the U.S., even when county-level vaccination numbers—the data policymakers consult—appear high enough to provide community protection.
A new study published in Nature Medicine reveals that pockets of low vaccination rates at the school level may be contributing to the rise in measles outbreaks in the U.S., even when county-level vaccination numbers appear sufficient for community protection. Before the COVID-19 pandemic, measles had been declared eliminated in the U.S. in 2000, but the virus began to spread again, reaching over 3,500 cases in 2025-26.
This increase was largely due to vaccine hesitancy, misinformation on social media, and varying vaccine exemption policies across states. Researchers analyzed publicly available county, school district, and school-level data on measles, mumps, and rubella (MMR) vaccinations, translating vaccination coverage into transmission risk using a mathematical model.
They found that a single case of measles could spread in a school with unvaccinated or partially vaccinated children, but this risk was largely hidden at the statewide and county-level when vaccination rates remained near the 95% herd immunity threshold. The study indicates that the average percentage of unprotected students across the country doubled from 5% to nearly 10% following the pandemic, emphasizing the need for more detailed data and school-level surveillance to understand and prevent measles outbreaks.
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