Gaines County is a vast, flat expanse far in the west of Texas: more than 1,500 square miles of sparsely populated farmland. And right now, this is the epicenter of a measles outbreak the likes of which this state hasn’t seen in more than 30 years.

A historic measles outbreak in West Texas is just short of 200 cases, Texas state health officials said Friday, while the number of cases in neighboring New Mexico tripled in a day to 30. Most of the cases across both states are in people younger than 18 and people who are unvaccinated or have an unknown vaccination status.