SEATTLE - Six of the 15 measles cases in Washington's outbreak came in San Juan County, which has a vaccination rate in schools of just 49 percent.
San Juan County public health officials say since the outbreak, people have rushed to get immunizations, after the first measles outbreak in the islands in 14 years.
Nationwide, the Centers for Disease Control and Prevention says measles cases this year have reached a 20-year high with 288 cases reported between Jan. 1 and May 23.
The CDC says the increase in measles cases is being driven by unvaccinated people who travel overseas, get infected and spread the virus in other communities of people that are unvaccinated.
Washington has been averaging between zero and five measles cases each year, but so far in 2014 has already had 15.
State Department of Health officials say six of those cases were in San Juan County and six in Whatcom County.
Snohomish, Skagit and Kitsap counties each had one resident infected.
"If you haven't been vaccinated or are not up to date on vaccinations this is the time to get vaccinated," said Dr. Jeffrey Duchin of Public Health Seattle and King County.
Duchin said claims that vaccines cause autism are false.
He said parents who choose not to vaccinate put their own kids at risk as well as vulnerable neighbors who can't be immunized for health reasons.
"When unvaccinated people congregate together it can spread and cause outbreaks," Duchin said.