The number of measles cases reported nationwide in 2019 is the highest in over 20 years, and the most since federal health officials declared the highly contagious disease eliminated in the United States in 2000.
More cases of measles can occur because of an increase in the number of unvaccinated travelers who become exposed to the disease overseas and its further spread in communities with low vaccination rates, according to the federal Centers for Disease Control and Prevention.
The high number of cases in 2019 is because a few large outbreaks that began in late 2018, the CDC says. There could be more large outbreaks, according to a study published in The Lancet that predicts which 25 U.S. counties are at highest risk for a measles outbreak.
The researchers write that reintroduction of the virus through travel to countries experiencing outbreaking and low vaccination rates fueled by non-medical exemptions are the two most salient factors for the 2019 outbreak.
The outbreaks that began in late 2018 include one in Washington state and two in New York. While the outbreak in Washington was declared over, the two outbreaks in New York, one in New York City and the second in Rockland County, are “the largest and longest lasting since measles was eliminated in 2000,” CDC Vaccine Director Dr. Nancy Messonnier said in a telephone briefing earlier this week.
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As of the latest update from the CDC, there have been 764 cases of measles reported in the United States and health officials expect more cases this year. On its website, the CDC says it is monitoring outbreaks in nine jurisdictions, which it defines as three or more cases.
According to the study published in The Lancet, 30 of the 45 U.S. counties that have reported measles cases in 2019 are included in the counties most at risk for an outbreak or are adjacent to one of the counties included in the list.
“Our prediction is aligned with multiple counties that have experienced measles outbreaks this year,” Lauren Gardner, an associate professor at Johns Hopkins University and an author of the study, said in a statement. “Critically, we recommend that public health officials and policymakers prioritize monitoring the counties we identify to be at high risk that have not yet reported cases, especially those that lie adjacent to counties with ongoing outbreaks and those that house large international airports,”
For example, Queens County in New York, ranked No.4 on the list, is adjacent to Brooklyn, New York, where there is currently a large outbreak of measles. Multnomah County in Oregon, ranked No.13 on the list, and is directly adjacent to Clark, Washington, where the outbreak in Washington was concentrated. The counties identified in the study where there has not been an outbreak yet is adjacent to a county that either has or is served by a major international airport.
Below are the counties most at risk of a measles outbreak identified in the study: