Health officials attributed the trend to declining rates of vaccination and people contracting the disease during travel to European countries such as Romania and Italy. But unvaccinated children tend to cluster together for many reasons. The current measles outbreak in Clark County and one diagnosed case in King County are examples of why the Measles, Mumps, and Rubella (MMR) Vaccine is a crucial requirement.
"During an outbreak is when you see an influx of patients who would otherwise be vaccine-hesitant", said Virginia Ramos, infection control nurse with Sea Mar Community Health Center, which runs six sites that offer vaccines in Clark County.
"The strain D8 in Washington's outbreak matches the strain from an ongoing Eastern European outbreak".
Ninety-two percent of the cases were reported by 10 countries: Ukraine (53,218), Serbia (5,076), Israel (2,919), France (2,913), Italy (2,517), Russian Federation (2,256), Georgia (2,203), Greece (2,193), Albania (1,466) and Romania (1,987).
Washington state Rep. Paul Harris (R-Vancouver) has introduced a measurethat would remove personal belief exemptions for the MMR vaccine.
While more children in Europe are being vaccinated against measles than ever before, progress has been "uneven" between countries and individual countries have some patches where vaccine take-up is low, it said. Among the confirmed cases, 43 were not immunized against the highly contagious disease.
Canada has been free of endemic measles since 1998, meaning the virus isn't constantly present.
World Health Organization said "uneven progress between and within countries" was to blame. If people aren't vaccinated, the virus can spread easily.
"We heard rumblings of a measles outbreak in the capital between December and January and I just knew we were going to get hit", Lon Kightlinger, a former South Dakota state epidemiologist and regular Peace Corp volunteer in Madagascar, tells CNN.
New data published on 7 February shows measles infection rates in Europe have tripled over the past year.
Gaps in vaccination coverage, complacency about the disease and a resistance by some parents to have their children immunised has been blamed for the concerning rise in infections. About 600 people a day were vaccinated during the last week of January, compared to 200 people during the same period past year. She notes that in many parts of the country, rates are only estimates, but even still, they point to signs of trouble.
Heidi Larson, a specialist in vaccines and public health at the London School of Hygiene and Tropical Medicine, said the increase in cases was a "wake-up call" on the importance of building confidence in vaccination.