Clark County, in Washington state, has declared a public health emergency because of a measles outbreak.
At least 21 people there are sick and the measles can be very dangerous, especially for young kids.
Of the 21 confirmed cases out West, 20 are children.
Health officials fear the highly contagious disease could spread to people in Oregon, as infected people went to several public places, including an NBA game.
So far, there are no confirmed cases from there.
Almost all the kids with measles were now vaccinated and that's a fact experts call "discouraging."
"This is a completely avoidable situation," said Dr. Anthony Fauci of the National Institutes of Health. "There's really, quite frankly, a tragedy, people are not vaccinating their children."
Fauci said misinformation on the internet and social media convinces some parents that vaccines are harmful, when in fact they save lives.
The nation's largest measles outbreak is in New York City's orthodox Jewish community, where 58 people have been infected.
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Measles outbreaks popping up across the country
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