A measles outbreak in West Texas has topped 120 cases and resulted in the first U.S. death from the illness in a decade.

At least 124 cases of measles have been identified in Texas since late January, mostly among children and teenagers who are either unvaccinated or whose vaccination status is unknown, officials say.

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.