An outbreak of measles in northwest Texas grew to 146 cases on Friday, two days after health officials reported that a child had died after being hospitalized in Lubbock. Twenty people have been hospitalized for treatment amid the outbreak,

In Texas, there were 146 cases of measles across the state and the South Plains, with 20 patients hospitalized. The best way to prevent getting sick is to get two doses of a measles vaccine.

Here’s what to know about the outbreak after the first U.S. death since 2015 from the highly contagious—but preventable—respiratory disease.