A rapidly growing measles outbreak in Gaines County, Texas, linked to low vaccination rates, has reached 48 cases, prompting urgent health warnings and vaccination efforts.

The measles outbreak first reported in Gaines County, Texas, has doubled to 48 cases since a count released earlier this week, the Texas Department of State Health Services said Friday. The first two cases were identified in late January and the numbers have been rising since.

The measles outbreak in the South Plains region, in West Texas, has expanded to at least 48 people, most of them children.