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

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.

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 outbreak to further spread in coming weeks.