Lancaster County in Pennsylvania has been the epicenter of the nation's worst measles outbreak in 35 years. It's also home to the largest Amish population in the U.S. Some Amish and related Mennonite groups, with historically lower rates of vaccination, have been hit hard. Vaccination rates also declined in the general population amid the resurgence of a contagious virus considered “eliminated” from the U.S. since 2000. Pennsylvania leads the U.S. this year with over 1,350 cases, more than a third in Lancaster County, according to official figures. Many Amish and Mennonites are showing a new openness to vaccines, while members of the general public are also taking extra precautions.