Texas health officials say the number of people with measles has increased to 146 in rural West Texas outbreak that led this week to the death of a school-aged child who was not vaccinated.

LUBBOCK, Texas (AP) — A person hospitalized with measles has died in West Texas, marking the first death in an outbreak that began late last month. Texas Tech University Health Sciences Center spokesperson Melissa Whitfield confirmed the death Wednesday. The age of the patient, who died overnight, wasn’t immediately clear.

Measles has been spreading across the U.S. for the last several weeks, sickening people in at least nine states amid a growing outbreak in western Texas. Several people have been hospitalized and at least one unvaccinated school-aged child in Texas has died,

Measles is a highly contagious airborne disease caused by a virus, and can be severe or even fatal. According to the U.S. Centers for Disease Control and Prevention (CDC), the best way to protect yourself against measles is to get vaccinated. Here, TIME answers all your questions about the vaccine.

Vaccination provides long-lasting 97% protection against measles infection. Most people who have been vaccinated do not need to be vaccinated again.

Measles had been largely eliminated entirely in the United States as of around 2000 thanks to vaccination and its consequent herd immunity, but unfortunately made a comeback in re