Zika Virus Infection Risks Calculated for Pregnant Women, Olympic Attendees in New Studies

First studies to estimate the risk of infection using mathematical models.

ByABC News
July 25, 2016, 5:00 PM

— -- Just weeks before the Olympics are slated to start in the nation at the center of the Zika virus outbreak, researchers have found new evidence about who is likely to contract the disease.

Two studies published today help shed light on the virus that the World Health Organization has called a "global health emergency." Yale researchers modeled the risk for people attending the Olympics and found only a small chance that those visiting Rio de Janerio for the Olympics would contract the virus.

Of the hundreds of thousands of visitors expected to visit Brazil for the Olympics, researchers found that just three to 37 attendees will contract the virus and then bring it to their home countries, according to the study published in the journal Annals of Internal Medicine.

The researchers conducted a mathematical model to understand the risks of an attendee contracting the virus. They examined multiple factors, including the spread of the dengue virus, spread by the same mosquitoes that spread Zika, during the World Cup and found that few people reported illness. They also noted that many travelers are coming from countries where the virus is already spreading.

"The possibility that travelers returning from the Olympics may spread Zika has become a polemic issue that has led to athletes dropping out of the event, and without evidence, undue stigmatization of Brazil. This study provides data, which together with initial findings from Brazilian scientists, show that these concerns may be largely exaggerated," Dr. Albert Ko, co-director of the Yale Global Health Justice Partnership and chair of the Department of Epidemiology of Microbial Diseases at Yale School of Public Health, said in a statement.

Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, said the modeling provides more evidence about who is most at risk for public health officials studying the outbreak.

"Any number of us have also been of the opinion of that the Olympics will offer low risk acquisition by people there and having them bring this infection home," he told ABC News today. "It's very, very nice to see that a group quietly and rigorously address this in a structured modeling fashion and have come up with an entirely similar conclusion."

Another modeling study published today investigated how many pregnant women either had been infected or are likely to be infected by the end of the recent Zika outbreak. The study, published in the journal Nature Microbiology, found that as many as 1.65 million pregnant women could be infected by the end of the "first wave of the epidemic."

Researchers from various institutions, including the Department of Biological Sciences and Eck Institute for Global Health at the University of Notre Dame, examined past viral outbreaks including chikungunya epidemics that are spread by the same mosquito that spreads the Zika virus to estimate how many pregnant women were likely to be infected. They also looked at different population demographics to estimate how many women were likely to be pregnant.

"Projections such as these have an important role to play in the early stages of an epidemic, when planning for surveillance and outbreak response is actively under way both internationally and locally," the authors wrote in the study.

They did not estimate how many infected pregnant women would give birth to children with microcephaly, a birth defect characterized by an abnormally small head and brain, which can lead to severe developmental disabilities.

Schaffner pointed out these kinds of modeling studies are important to help react to the virus, but that experts are still unsure if the virus will remain endemic to certain areas after the explosive outbreak or if it will largely die out.

"We look forward to another rigorous modeling study," in this area, he said. "We think Zika infection has been so pervasive" it might cause one big year of infections "and then smoldering cases subsequently."

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