Delaware Dipped Below the Herd-Immunity Line. Measles Followed.

Delaware's kindergarten MMR vaccination rate fell from 98.5% in 2016 to 94.1%, dropping below the ~95% threshold needed for herd immunity — the coverage level that keeps a disease from spreading widely. In July, the state logged its first measles case in over a decade; two days later, five cases were declared an outbreak. Nationally, 2,371 cases by July 30 set a 35-year high.