Can county vaccination numbers tell you if your child’s school is protected?
No. This study found that measles risk inside individual schools crossed the epidemic threshold in 2022-2023, and that shift was invisible in the county-level numbers public health agencies watch.
The United States declared measles eliminated in 2000. In 2025-2026, more than 3,500 cases put that status under formal review. The researchers behind this paper wanted to know why the warning never came in time, and their answer is about the size of the map, not the size of the problem.
How the researchers looked at it
The team assembled a nationwide vaccination database covering 45 US states and Washington, DC, from 2013 to 2025. It included more than 50,000 schools, 13,000 school districts and 3,000 counties. They then built a transmission model to estimate epidemic risk at each of those scales separately.
The key measure is the effective reproduction number. In plain terms, it is the average number of new cases one infected person creates. Below 1, an outbreak fizzles out. Above 1, it grows. That line is the epidemic threshold, and where you draw your map decides whether you can see it being crossed.
What the data show
Average susceptibility, meaning the share of children without protection, doubled from roughly 5% to about 10% after the pandemic. In everyday terms, a classroom that once had about 5 unprotected children in every 100 now has about 10.
School-level effective reproduction numbers crossed the epidemic threshold in 2022-2023. The authors describe that transition as invisible to aggregated surveillance. County-level averages, the figures agencies actually monitor, did not register it, because averaging thousands of children across a whole county blends the schools with very low coverage into the schools with very high coverage until the danger disappears from the spreadsheet.
The paper also found something less obvious. County lines do not match how people actually live and move, and that mismatch creates what the authors call cross-boundary corridors. Through those corridors, spillover from less-vaccinated populations can push a well-vaccinated county above the threshold. Being surrounded by good numbers is not the same as being safe.
State trajectories diverged sharply over the study period, and the researchers link that divergence to exemption policies and vaccination infrastructure rather than to anything about the virus itself.
Dr. Kumar’s Take
The most useful idea in this paper is that a measurement problem can look exactly like a safety report. For years, county coverage figures said the buffer was holding. The buffer was not holding. It had already failed in specific schools, and the average smoothed the failure into invisibility.
Measles is among the most contagious infections known, and that is precisely why averages fail here. A disease that spreads this efficiently does not need a whole county to be undervaccinated. It needs one building where enough unprotected children sit together all day. Averaging is a reasonable tool for conditions that spread slowly and evenly. Measles is neither.
The doubling of susceptibility from about 5% to 10% is the number I would keep. It is not a dramatic figure on its own, and that is the point. Modest-sounding erosion, concentrated in the wrong places, is enough to move schools from containment to sustained spread.
This is modeling work, not a count of infections, and a transmission model rests on assumptions about how people mix. What the model cannot tell you is exactly when or where the next outbreak lands. What it does tell you is that the data being collected are the wrong shape for the question being asked.
Questions this raises
The authors argue that preventing measles from becoming endemic again requires surveillance and action at the school and district level, where an imported case can be intercepted before it starts sustained transmission. That is a real operational change, not a slogan. It means publishing and acting on coverage figures for individual schools rather than reporting a county number and calling it monitoring.
It also raises a fairness question the paper touches on through its spillover finding. A family that vaccinates on schedule, in a district with strong coverage, still carries risk imported across a boundary they never think about. Protection at this scale is shared, and the map that reports it should match the map people actually live on.
Practical Takeaways
- Ask your child’s school or district for its own MMR coverage rate, since the county figure can look reassuring while a single school sits well below the level needed to stop spread.
- If your family’s vaccinations are behind schedule, catching up is the one part of this you fully control, and it is worth a conversation with your child’s doctor.
- Treat a low school coverage number as information about local risk during an outbreak, not as a reason for alarm on an ordinary week.
- Remember that neighboring communities matter, because this study found that spillover across county lines can push even well-vaccinated areas above the outbreak threshold.
Related Studies and Research
- 1952: the year polio struck 57,879 Americans, a record-breaking epidemic
- Shingles vaccine cuts heart attack risk nearly in half for heart disease patients
- Insomnia plus sleep apnea raises heart disease risk nearly 4-fold
- Why perimenopause triggers first-time depression in healthy women
FAQs
What does “measles elimination” actually mean if cases still happen?
Elimination does not mean zero cases. It means the virus is no longer continuously circulating inside the country, so infections that do appear are traced back to travel and then stop. Cases arrive, infect a few people, and die out. Losing elimination status means the chain no longer breaks on its own and the virus starts sustaining itself locally again. That is the specific outcome this paper is warning about, and it is why the 2025-2026 case count triggered a formal review.
Why is a 10% susceptibility rate considered dangerous when 90% are protected?
Measles spreads far more efficiently than most infections, so the share of a group that must be immune to stop transmission is unusually high. The study’s own approach reflects this, since it tracked whether school-level transmission crossed the epidemic threshold rather than judging coverage against a fixed target. A group can look well protected on paper and still support spread if the unprotected children are clustered together instead of scattered. Concentration is what makes a modest percentage dangerous.
Does this study say vaccine exemption laws caused the problem?
Not directly. The researchers report that state trajectories diverged markedly over the study period and describe those differences as shaped by exemption policies and vaccination infrastructure. That is an association drawn from coverage data across states, not an experiment isolating the effect of any one law. The broader driver named in the paper is vaccine hesitancy, accelerated by COVID-19 disruption and misinformation.
Bottom Line
This paper makes a narrow and serious point. Across more than 50,000 schools in 45 states and DC, the share of unprotected children roughly doubled from about 5% to 10% after the pandemic, and school-level transmission risk crossed the epidemic threshold in 2022-2023. County averages, the numbers the system relies on, never showed it. The warning existed in the data all along, at a scale nobody was reading.
