An ongoing measles outbreak in Pennsylvania has quickly become the largest and deadliest in the United States in more than 30 years.
Historical data suggests that 1 to 3 people will die out of every 1,000 unvaccinated people who contract measles. But Pennsylvania has reported five measles-associated deaths — with a sixth under review — out of about 1,300 total reported cases since the start of the outbreak in April.
