Gaines County in West Texas is at the heart of the ongoing measles outbreak. Non-medical vaccine exemption rates there are high.

The effectiveness of the vaccine, coupled with rising vaccination rates, led to such low rates of measles that it was declared eliminated in the U.S. in 2000. In recent years, though, the virus has made a resurgence, as childhood vaccination rates have dropped nationwide.

A child who wasn’t vaccinated died in a measles outbreak in rural West Texas, officials there said Wednesday, the first U.S. death from the highly contagious respiratory disease since 2015.