A measles outbreak in Texas has grown to 90 cases, mostly among unvaccinated children, state health data published Friday shows.

The largest measles outbreak in Texas in more than 30 years showed no signs of slowing down on Friday, rising to 90 cases across seven counties. The increase represents a jump of more than 50% since the Department of State Health Services last released an update on Tuesday.

The measles outbreak in Texas has escalated sharply to 90 cases as health officials worry about the spread to more communities.