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There are now 102 people in 14 states who have become infected with the extremely contagious virus that is considered vaccine-preventable, according to the CDC. Most, but not all cases, have been linked to several dozen people who were exposed to the measles at Disneyland in Anaheim, California, and were not vaccinated.
"Although we aren't sure exactly how this year's outbreak began, we assume that someone got infected overseas, visited the parks and spread the disease to others," Dr. Anne Schuchat, who directs the National Center for Immunization and Respiratory Diseases, said during a news conference Thursday.
Of the 34 people for whom the California Department of Public Health had vaccination records, only five had received both doses of the measles vaccine, according to the department. One received just the first dose. Nationally, officials are seeing the same trend, Schuchat said last week.
"This is not a problem with the measles vaccine not working," she said. "This is a problem of the measles vaccine not being used."
The CDC is seeing more adult cases of measles than usual during this outbreak, Schuchat said, adding that children are getting the virus, too.
Cases have now been reported in Arizona, California, Colorado, Illinois, Minnesota, Michigan, Nebraska, New York, Oregon, Pennsylvania, South Dakota, Texas, Utah and Washington, according to the CDC. The CDC issued a health advisory Jan. 23, at which point the virus had only spread to six states beyond California and Mexico.
The United States last year reported its highest number of measles cases in two decades with 644 cases as part of 20 separate outbreaks, attributing the spike to a measles outbreak in the Philippines and overseas travelers.
The 102 cases reported between Jan. 1 and Jan. 30 this year are considered part of one outbreak.
The measles virus is contagious long before symptoms appear, and it is airborne, according to the CDC. One infected person with the measles can spread it to an average of 18 other people, and it can linger in the air and live on surfaces to spread after an infected person has left a room.
Complications include hearing loss, pneumonia and swelling of the brain, according to the CDC. About one or two people out of every 1,000 people infected with the measles will die.