The measles outbreak first reported in Gaines County, Texas, has doubled to 48 cases in the last four days, the Texas Department of State Health Services said in a statement Friday.

The outbreak in Gaines County, with a population of about 22,000, has grown since two cases were reported in January. All those who contracted measles were unvaccinated, health officials said.

The measles outbreak in West Texas has doubled to 48 cases.42 cases have been reported in Gaines County.Surrounding counties have reported the other six cases.