A measles outbreak in Kansas has more than doubled to nearly two dozen cases over the last week, according to state health officials, who said they identified a “possible link” between confirmed cases of the highly contagious illness and a larger outbreak in Texas and New Mexico.

State health officials worry that declining vaccination rates have left many communities vulnerable nationwide.

The Texas health department said on Friday that the number of measles cases in the state rose 20% since its last report three days ago, as experts warn they expect the