Measles was officially declared eradicated in the U.S. more than 20 years ago, but new outbreaks of the disease are popping up — and experts say declining vaccination rates are jeopardizing herd immunity and increasing the risk.
In Philadelphia, nine cases were reported after a cluster started in a hospital and spread to other medical facilities and a day care center. Measles is a highly contagious and potentially deadly virus that causes a tell-tale rash.