Delaware

Delaware is a small Mid-Atlantic US state on the Delmarva Peninsula, one of the original thirteen colonies and the first state to ratify the US Constitution. It is distinct from Delaware County, Pennsylvania, where an earlier wastewater measles signal was separately retracted as a false positive.

In July 2026 Delaware declared its first measles outbreak in over a decade, four confirmed cases, amid a national resurgence whose 24 July count, 2,318, already exceeded every case reported across the whole of 2025 (2,289). It was not yet confirmed whether the outbreak connects to an earlier unvaccinated case reported in Kent County the same week. The outbreak's small size relative to Utah's or Pennsylvania's caseloads makes it notable chiefly for ending a decade-long absence of confirmed measles transmission in the state.