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.

At least 49 cases have been confirmed. Health officials — who are scrambling to get a handle on the vaccine-preventable outbreak — suspect 200 to 300 people may be infected.

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.