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There is a debate going on about this summer's Olympic Games. Nearly 200 scientists have signed a letter to the World Health Organization calling for the games to be moved out of Rio de Janeiro. They're worried visitors to the Olympics will catch the Zika virus and take it back home and cause new outbreaks. The WHO has resisted their calls. NPR's Michaeleen Doucleff looks at the science to evaluate the risks.
MICHAELEEN DOUCLEFF, BYLINE: One researcher who wants the Olympics moved is Arthur Caplan, a bioethicist at New York University. He helped write the letter to WHO. The WHO disagreed, saying there was no health reason to move the Olympics. But Kaplan says the stakes are just too high.
ARTHUR CAPLAN: I think it's ethically dubious to run the Olympics when you've got a epidemic with a virus that we don't understand very well. There's just a lot that, apparently, we don't know.
DOUCLEFF: Like how long Zika can linger in the body or how big of a problem sexual transmission is. Scientists don't know that much about Zika. It only emerged as a problem a few years ago. But it can cause devastating birth defects, so Kaplan says, err on the side of caution. But here's another thing - Zika is spread by mosquitoes, and scientists do know a lot about how that works. They can even predict how many mosquitoes will be in Rio during the games. That's exactly what biologist Mikkel Quam has been working on at Umea University in Sweden. He built a computer model to estimate the chance fans and athletes will get bitten by a mosquito. I talked to him on Skype, and he says his results were much lower than he expected.
MIKKEL QUAM: I was legitimately surprised. There's very little mosquito activity during the Olympics.
DOUCLEFF: Quam found that only 4 percent of people at the Olympic Games will get a mosquito bite. The chance they'll get bitten by a mosquito carrying Zika is even lower - much, much lower.
QUAM: I think we could get cases, but I don't expect many cases.
DOUCLEFF: Quam says it's hard to calculate the exact number, but a preliminary model suggests, at most, 16 people will get infected with Zika during the Olympic Games - 16 out of the half-a-million attendees. Alessandro Vespignani at Northeastern University agrees with Quam's prediction. He says fans and athletes are much more likely to get the flu and food poisoning than Zika.
ALESSANDRO VESPIGNANI: You know, if I would be an athlete competing, from what I've read, I would be more worried about the pollution in the water than Zika.
DOUCLEFF: But, Vespignani says, whether the games pose a danger to the world isn't just about the number of Zika cases. It's also about where those cases go. What's the chance a fan brings the virus home and triggers a new outbreak in another country? So Vespignani is working on a computer model for the U.S. government to predict how Zika will spread both here and around the world. He added the extra travelers from the Olympics and ran the models again. What he saw was reassuring. Keeping the games in Rio doesn't seem to change the course of the epidemic.
VESPIGNANI: There are already so many cases around the world, you know, that adding a little bit more of cases is not making a difference at this point.
DOUCLEFF: So there's no reason to move the games because of Zika?
VESPIGNANI: Yeah, I agree with the WHO statement on this.
DOUCLEFF: The Centers for Disease Control and Prevention's director, Dr. Thomas Frieden, told reporters that travelers to the Olympics will make up just a tiny fraction of people coming in and out of Zika-infected areas.
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THOMAS FRIEDEN: So even if you were to say the Olympics weren't to happen, you'd still be left with 99.75 percent of the risk of Zika continuing to spread.
DOUCLEFF: So right now, the CDC agrees the games should stay in Rio. Michaeleen Doucleff, NPR News.
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