Measles Resurgence in the U.S.: Declining Vaccination Rates Fuel Outbreak Risk
Measles, once considered eliminated in the United States, is making a concerning comeback. New analyses of nationwide vaccination data reveal a quiet erosion of immunity, creating conditions ripe for large outbreaks. Experts warn that relying on county-level vaccination averages obscures critical vulnerabilities at the school level, hindering effective prevention efforts.
The Decline in Vaccination Coverage
Researchers at Cornell University, led by assistant professor of infectious disease ecology Ana Bento, PhD, have been at the forefront of investigating this resurgence. Their work, including recent pre-print papers, highlights a significant drop in measles immunity following the COVID-19 pandemic. Bento and her team assembled the most detailed school-by-school measles-mumps-rubella (MMR) vaccination database to date, utilizing a new transmission model to assess the potential for outbreaks in different communities.
“We found that, after the Covid-19 pandemic, the share of children vulnerable to measles roughly doubled from about 5% to 10%,” Bento explains. “And in 2022–2023 many schools reached levels where a single measles case can trigger ongoing transmission, even though their counties still appear ‘safe’ on paper.”
The Problem with County-Level Averages
A key finding from Bento’s research is that averaging vaccination rates across entire counties masks significant disparities. Slight, highly under-vaccinated schools are effectively hidden within these broader averages, creating a false sense of security. This is particularly problematic in areas where school district boundaries don’t align with county lines, allowing outbreaks to spread across administrative borders.
“Our team shows that averaging vaccination rates across whole counties hides small, highly under-vaccinated schools and creates a false sense of security, especially where school-district boundaries cut across county lines and allow outbreaks to jump into neighboring, otherwise well-vaccinated areas,” Bento states. “We argue that to prevent measles from becoming re-established in the U.S., public health agencies need to track and respond to vaccination gaps at the school level, the scale at which vulnerability actually accumulates, instead of relying on coarse county-wide averages.”
Case Studies: Texas and South Carolina
Further research from Bento’s lab compared two contrasting measles outbreak scenarios: Gaines County, Texas, where a 2025 outbreak was successfully contained after 414 cases, and Spartanburg County, South Carolina, where an outbreak that began in 2025 has surpassed 900 cases and remains ongoing.
Using detailed school and district vaccination data and spatial mapping, the researchers discovered that the peak density of unvaccinated students in Spartanburg was approximately six times higher than in Gaines County (roughly 23 versus 4 unvaccinated children per square mile). This created a continuous corridor of under-vaccinated schools, facilitating the persistent spread of infection. In contrast, unvaccinated students in Gaines County were concentrated in a single, relatively isolated school district, limiting the outbreak’s reach.
The Need for School-Level Data and Targeted Interventions
Bento’s research underscores the urgent need for public health agencies to access routine school-level vaccination data and implement tools capable of identifying clusters of under-vaccinated children before they can seed long-running outbreaks. This shift in surveillance strategy is crucial to preventing the re-establishment of measles in the U.S.
“In another new study, we demonstrate that county-wide vaccination statistics can hide large differences in local outbreak risk, and it argues that to understand and prevent future measles surges, public health agencies need routine access to school-level vaccination data and tools that can identify clusters of under-vaccinated children before they seed long-running outbreaks,” Bento explains.
Key Takeaways
- Measles is making a concerning comeback in the U.S. Due to declining vaccination rates.
- County-level vaccination averages can be misleading and hide critical vulnerabilities at the school level.
- Targeted interventions and school-level data are essential for preventing outbreaks.
- The COVID-19 pandemic contributed to a doubling of the percentage of children susceptible to measles.
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