Washington state has declared a state of emergency as a measles outbreak spreads in two counties.

NPR reports that as of Monday the Washington Department of Health found 36 known and 11 suspected cases. The growing number alarmed Governor Jay Inslee so much so that he announced the state of emergency.

On Friday, Gov. Jay Inslee said, “The measles virus is a highly contagious infectious disease that can be fatal in small children, and the existence of 26 confirmed cases in the state of Washington creates an extreme public health risk that may quickly spread to other counties.”

The Clark County Public Health department investigated the measles outbreak and concluded that 31 of the confirmed cases were not immunized. The county still has yet to investigate the other cases. One confirmed adult case was found in King County, but the man recovered. He admits to traveling to Clark County, where many officials suspect he was infected.

Measles is particularly dangerous to individuals who have compromised immune system, and epidemiologist Scott Lindquist told NPR many of these infected patients traveled outside the country to very public places. “Folks that are immuno-compromised — pregnant women, young kids and those that are unvaccinated — could be at risk for this disease,” Lindquist said. The symptoms don’t appear until after a couple of days.

At least 25 of the cases are infected children under the age of 10 years old. In 2017, the country had 120 reported cases. This number tripled to 349 cases in 2018.

The Centers for Disease Control and Prevention considered measles eliminated in the U.S. in the 2000s, and state laws allowing parents to override mandated vaccinations quickly followed.

Washington is one state that gives parents the ability to reject any school mandated vaccination for measles, mumps and rubella for their children for non-medical reasons.