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

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

## Details

**Authors** Chen et al.

**Year** 2026

**Publisher** Nature Medicine

**Discipline** Public Health

**Secondary disciplines** Medicine

[Read it at the publisher](https://doi.org/10.1038/s41591-026-04612-2) 
10.1038/s41591-026-04612-2

## In authors' words

### 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.

## Commentary

### 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.

**Patterns it shows** D, S

**Added** 2026-08-23

**How to cite this** Chen et al. (2026). County surveillance failed to detect that measles transmission reached epidemic threshold in schools. Nature Medicine.