A growing measles outbreak in Texas has 90 confirmed cases — a jump from a few days ago. The virus is spreading primarily among people who are unvaccinated or whose vaccine status is unknown.

The U.S. Centers for Disease Control and Prevention on Friday reported that measles cases so far this year had jumped to 93 from 14 a week ago, mainly driven by an outbreak in Texas. The Texas Department of State Health Services said last week that more cases of the highly contagious disease were likely to surface due to an outbreak in Gaines County.

Texas' measles outbreak is up to 90 cases. Here's what you need to know about the virus, vaccination and boosters.