A rapidly escalating measles outbreak in West Texas has forced some private schools to close their doors. Local health departments, already stretched thin, are prioritizing efforts to contain the highly contagious virus.

As of Tuesday, 24 cases were identified in Gaines County, with nine patients hospitalized. All of the cases are unvaccinated, DSHS reported.

This is the tip of the iceberg,” said Rekha Lakshmanan, chief strategy officer for The Immunization Partnership in Houston, a nonprofit that advocates for vaccine access. “I think this is going to get a lot worse before it gets better.