Measles

Congenital measles is alarming but narrow: the baby's risk hinges on a mother's rash near delivery, and each protective step has its own deadline. What Pennsylvania doctors were told, and what no one has counted.

Four fully vaccinated Pennsylvanians caught measles as the state's outbreak topped 676 cases — a reminder that a 97% effective vaccine was never advertised as 100%.

Measles cases in the U.S. have already topped last year's total, and Pennsylvania just recorded the country's first deaths from the disease in 35 years. The reason it keeps returning comes down to one number: 95%.