Chicago, Los Angeles and Miami are the cities most likely to see the next measles outbreaks, according to an unusual new study.
Researchers at the University of Texas at Austin and Johns Hopkins University mapped the 25 American counties most at risk of measles because of their vaccine-exemption rates and proximity to airports.
A similar map published last year proved surprisingly accurate at forecasting many of this year’s cases. But both groups of scientists failed to predict the measles outbreak that began in Brooklyn, currently the nation’s largest.
These prediction models need refining, one expert noted, and the Centers for Disease Control and Prevention should make it a priority in order to get ahead of measles cases.
The study, published this week in The Lancet Infectious Diseases, found that Cook County, which includes Chicago, was likeliest to experience a measles outbreak. Los Angeles and Miami-Dade counties were next, followed by New York’s Queens County and the counties that include the cities of Seattle, Phoenix, Fort Lauderdale, Las Vegas, Houston and Honolulu.
To assess risk, the researchers looked at how many children in counties across the country had nonmedical vaccination exemptions — which include “religious,” “philosophical” or “personal belief” exemptions, depending on state law.
The team then focused on counties with international airports, because every American outbreak since 2000 has begun with a case imported from overseas.
They gave greater weight to airports with many passengers arriving from countries with thousands of measles cases, including India, China, Mexico, Japan, Ukraine, the Philippines and Thailand.
However, both studies failed to foresee what is now the country’s largest outbreak — the one among Orthodox Jews in the Williamsburg neighborhood of New York — which is in Brooklyn, not Queens.
(The Lancet authors said their forecasts were correct about two-thirds of the time, as long as counties “spatially adjacent” to the ones they saw as potential hot spots were included.)
In September last year, the virus spread from Ukraine to Orthodox Jewish communities in Israel. One month later, Orthodox Jews from New York carried measles almost simultaneously to Brooklyn and to suburban Rockland County, N.Y. The outbreak spread from New York to Orthodox communities in Michigan.
“What we did not calculate at all was that it would come from Israel,” said Sahotra Sarkar, a professor of philosophy and integrative biology at the University of Texas at Austin and a co-author of the new study.
A similar study published last June in PLOS Medicine ranked the risk of measles outbreaks in 18 states with philosophical or personal belief exemptions to vaccination. The research was prescient: almost half the “hotspot” metropolitan areas the scientists noted — particularly Washington State, Texas and Michigan — saw outbreaks this year.
“In the major leagues, that’s an all-star batting average,” said Dr. Peter J. Hotez, a director of the Texas Children’s Hospital Center for Vaccine Development and a co-author of the PLOS Medicine study.
Dr. Hotez and his colleagues did not look at New York State because it does not have “philosophical” exemptions to vaccination, although the state permits religious ones — a loophole that the legislature is considering eliminating.
“What I never expected was an outbreak in Jewish communities,” Dr. Hotez joked. “In my book, Jews make the vaccines.” (Dr. Hotez, who is Jewish and researches vaccines against tropical diseases, cited such pioneers as Albert Sabin, Jonas Salk, Stanley Plotkin and Rachel Schneerson.)
To refine their predictive models, both Dr. Hotez and Dr. Sarkar said they would need to learn to account for the fact that vaccination rates are not evenly spread out across urban counties; low rates tend to cluster in smaller ethnic, religious or educational communities.
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In the last five years, according to the C.D.C., 75 percent of measles cases have occurred in tight-knit communities, such as Somalis in Minneapolis, the Amish in Ohio and Orthodox Jews in Brooklyn.
This year’s measles outbreak in Washington State’s Clark County, near Portland, Ore., includes 72 cases linked to Russian-speaking immigrants from the former Soviet Union, according to a Vox article citing C.D.C. sources. Many of the immigrants were skeptical of government medical requirements, including vaccination.
Near Austin, Tex., Dr. Sarkar said, vaccination rates are lowest among children attending Waldorf schools and a few charter schools where families reject vaccination.
Many are influenced, he said, by Andrew Wakefield, the former British doctor who started the misconception that the measles vaccine causes autism, even though that research was discredited long ago.
After losing his medical license, Mr. Wakefield moved to Austin, where he directs films condemning vaccination.
“He has a very well-heeled following here,” Dr. Sarkar said.
The Austin area is number 22 on his list of places most likely to see a measles outbreak.
