Measles outbreaks are most likely occur in Chicago, Los Angeles, and Miami this year, according to a study published last week in The Lancet Infectious Diseases. As The New York Times reports, researchers at the University of Texas, Austin, Johns Hopkins University, and collaborators elsewhere ranked US counties by risk of a 2019 measles outbreak, taking into account vaccination exemptions for non-medical reasons and proximity to international airports, and these three metropolitan areas topped the list.
As of April 15, two-thirds of the US counties that have had measles outbreaks this year were either among the 25 that the researchers predicted as having the highest measles risk or were adjacent to those counties.
The study did not directly predict the largest measles outbreak so far this year, which is centered within the Orthodox Jewish community in Williamsburg, Brooklyn. Brooklyn (Kings County) is, however, adjacent to Queens County, which was fourth on the researchers’ risk list. Another study making similar predictions, published in PLOS Medicine last June, also failed to foresee the Williamsburg outbreak.
The infections in Williamsburg began last fall, when measles spread from Ukraine to Orthodox Jewish communities in Israel and from there to the Orthodox Jewish community in Williamsburg and in Rockland County, New York, according to the Times. From New York, measles spread to Orthodox Jewish communities in Michigan.
“Basically, a measles outbreak only happens if there are two things in play. There has to be a group of unvaccinated individuals, and there has to be the introduction into that area,” study coauthor Lauren Gardner, an associate professor of civil engineering at Johns Hopkins University, tells Gizmodo. Measles was declared eliminated from the US in 2000, so any introduction would have to come from outside the country.
To account for both of those factors, the study authors assigned a higher risk score to counties with airports welcoming travelers from countries with high measles rates, the Times notes, but Israel was not one of the countries on the radar.
“What we did not calculate at all was that it would come from Israel,” study coauthor and University of Texas professor Sahotra Sarkar, tells the Times.
Counties on the list should increase measles surveillance and vaccination efforts, write the authors of the Lancet Infectious Diseases study.
To improve future risk assessments, researchers from both studies tell the Times, models should account for the clustering of low vaccination rates within particular communities that are bound by religion, ethnicity, or education.