[DSRP Evidence](https://dsrpevidence.org/)

# County surveillance failed to detect that measles transmission reached epidemic threshold in schools

Chen et al., 2026, Nature Medicine — Public Health

Patterns: [Distinctions](https://dsrpevidence.org/pattern/distinctions), [Systems](https://dsrpevidence.org/pattern/systems)

## In short

An aggregate (the county) can sit safely below a critical boundary while its own parts (individual schools) have already crossed it, so the whole conceals what its parts reveal.

## What they found (results)

School-level analysis of vaccination records from over 50,000 US schools showed transmission risk crossed the epidemic threshold at the school level 2-3 years before the 2025-2026 outbreaks, while county-level aggregated estimates always remained below that threshold.

These researchers were not testing DSRP. The finding is theirs; the correspondence to DSRP is drawn by this site.

[Source](https://doi.org/10.1038/s41591-026-04612-2)