FRESNO, Calif. (KFSN) -- From New York to nearby Washington, ten states across the country are grappling with the measles.
Even though high vaccination rates protect Fresno County, doctors at Valley Children's Hospital feel uneasy.
"It's incredibly disappointing, and it's tragic when we have children who lives may be lost," said Dr. Karen Dahl.
More than 97-percent of the Valley is vaccinated -- that's higher than the national average.
RELATED: Patients in Northwest measles outbreak traveled to Hawaii
But doctors say in an era of travel it's easy for the virus to travel quickly.
Last May, a man who traveled out-of-state came back with the measles.
"For Fresno County, one case is enough to spark an outreach or to spark some type of response, an emergency response," said Leticia Berber with the Fresno County Department of Public Health.
Measles is as highly contagious as a disease can get. If someone infected coughs or sneezes, it can live in the air for up to two hours. If one person has it, they can infect 90 percent of the people around them, if they aren't vaccinated.
"You can pass the measles disease even before knowing you have it," said Dr. Dahl.
Experts say states with the largest outbreaks also have the most significant pockets of anti-vaxxers.
RELATED: Measles: Symptoms, vaccine and treatment
500 kids died every year in the U.S. before the vaccine.
Doctors say parents have unfortunately forgotten the risk because they don't see those deaths anymore.
"There is no evidence it is linked to autism. But even the discussion that began about that years ago stuck in people's minds. And so people still have a concern, and they don't really see the benefit when they haven't seen the real risk," Dr. Dahl said.
The measles vaccine, known as the MMR, is very effective.
One dose is about 93% effective at preventing measles if you come in contact with the virus.
Measles starts off like a cold. A rash then appears several days later.
If you even suspect your child may be showing symptoms, doctors say to give them a call immediately.
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