Inslee's proclamation allows agencies and departments to use state resources and "do everything reasonably possible to assist affected areas".
Gov. Jay Inslee said in a statement that the outbreak in Clark County "creates an extreme public health risk" that could spread throughout the state.
Health officials in southwestern Idaho are warning medical care providers to be on the lookout for symptoms of measles because of an outbreak in western Washington that has sickened at least 26 people.
"Routinely we don't vaccinate children prior to the age of one, so infants are likely to be susceptible, especially after about four to six months of age", she says.
Health officials say a suspected measles case in King County has been confirmed. For now, public health officials are focused on preventing additional exposure.
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Officials there say they expect more cases. The measles vaccine is very effective.
Clark County has already spent more than $100,000 trying to contain the outbreak, and staff is being pulled from other duties, including restaurant inspections, he said.
Clark County, which includes the Portland bedroom community of Vancouver, Washington, has a measles vaccination rate of 78 percent, well below the 92 to 94 percent rate required for so-called "herd immunity", said Marissa Armstrong, the department's spokeswoman. The typical recommendations are that children should get two doses of MMR vaccine, the first between 12 to 15 months of age and the second between 4 and 6 years old.
Those who may have been exposed should watch for early symptoms of fever and malaise and then a rash starting on the head and moving down the body.
"Because measles is contagious before people realize they are sick, those who are not vaccinated may spread the disease without knowing".
Measles is highly infectious and spreads through the air by coughing and sneezing, as well as respiratory secretions.