Washington Gov. Jay Inslee declared a state of emergency Friday over 31 cases of measles in the state.

The declaration allows the state to request medical resources from other states and tells state agencies to do everything possible to help workers who are treating people with measles and trying to stop the spread of the highly contagious disease.

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

Clark County announced Friday that there are 30 confirmed measles cases in the Vancouver area. One person in King County has also been diagnosed.

There are nine more suspected cases in Clark County. The majority of the people who are infected are children 10 years old or younger.

The emergency declaration shows the severity of an unusually large outbreak. Washington has not seen an outbreak of this size in recent memory and public health officials expect the number of people affected to climb in the next months.

Measles is highly contagious and can linger in the air after an infected person has left the area for up to two hours. The state’s emergency declaration says that anyone who hasn’t been vaccinated and comes in contact with an infected person will likely get the disease.

Washington and Oregon do not have enough people who have received vaccines to achieve what scientists call “herd immunity,” which can stop a disease’s progression before it starts.

The measles vaccine is 97 percent effective and the Washington health department tries to provide it for little to no cost to people who can’t afford it.