Health and Science

Yale report finds low risk of Zika spreading around world due to Rio Olympics

A doctor performs physical therapy on an infant born with microcephaly in Recife, Brazil.
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If you're headed to Rio next month for the Olympic Games, you'll have a very, very low chance of catching the Zika virus, a new report says. And your chance of actually bringing the virus back home will be even lower.

A new Yale School of Public Health report suggests that even in the worst-case scenario, only a handful of Americans — at the very most — are likely to be infected with the Zika virus and bring it back with them if they travel to the Summer Games in Brazil.

And there's a fair chance, statistically speaking, that no Americans will travel to the United States with the virus after attending the Olympics in the country that has been most affected by Zika, according to the authors of the paper published in the Annals of Internal Medicine.

The paper estimates that out of the many thousands of international travelers from all countries who go to the Olympic and Paralympic Games in Rio next month and in September, only between six people — on the low end — and 80 people — on the high end — are likely to become infected by Zika.

And because Zika naturally clears from infected people over time, the authors estimate "the total number of infected travelers returning to all countries to be between 3 ... and 37," according to their paper, which is based on statistical modeling.

"The risk is low," said Joseph Lewnard, a researcher at the Yale School of Public Health, and one of the three co-authors of the paper.

The paper comes as some athletes have said they will not attend the Games, and two months after 150 doctors, bioethicists and scientists called for the Games to be either postponed or moved because of the Zika outbreak in Brazil.

Zika, which is primarily spread by mosquitoes but also can be transmitted via sex, has infected more than 120,000 people in Brazil, and led to nearly 1,700 cases of congenital malformations including abnormally small heads in newborns.

Lewnard said the paper doesn't argue that Zika isn't a legitimate health threat.

In addition to microcephaly in newborns, Zika can cause Guillain-Barre syndrome, an autoimmune disease that leads to muscle weakness. The federal Centers for Disease Control and Prevention has urged pregnant women not to travel to any area with Zika.

"The threat of Zika is a concern. It's a public health crisis," said Lewnard.

"It's just that canceling the Olympics is not going to be what it takes to stop the problem here," he added.

There have been about 1,400 cases of Zika reported in the United States — the vast majority of which are travel-related. A total of 400 of those cases involved pregnant women with lab evidence of Zika infection, according to the CDC. There has been one Zika-related death in the United States, of an elderly patient in June. A 70-year-old man in Puerto Rico died in February of complications from the virus.

Although those cases have drawn widespread media attention in the U.S., the new paper estimates that an individual international traveler to the Games in Rio will have a probability of acquiring Zika from 1 in 6,200, at the high end of risk, to just 1 in 56,300 at the low end.

And the probability of taking the virus back to their home country is significantly lower, given the claim that Zika will clear a person's system in around 10 days, on average.

The paper noted that most travelers, more than 50 percent, to the games, will be from the U.S., Canada, Europe, Oceania, Japan, South Korean and Israel, "where the overall risk of local mosquito-borne transmission is expected to be low."

Arthur Caplan, a bioethicist at New York University, was critical of the new report, saying "it makes the usual conservative assumptions" to calculate the risk of Zika infection among travelers.

Caplan said he believes the authors are underestimating the numbers of cases that will occur, as well as the time that the virus stays in a person's blood, and the number of people who will be carrying Zika to Rio from their own countries, who themselves can transmit the virus to other travelers.

Caplan was one of the signatories to a letter in May that urged the World Health Organization to pressure Olympics officials to move or postpone the Games because of Zika.

Now, with the opening ceremonies due to take place Aug. 5, in less than two weeks, "I understand they're not going to move the Games, or postpone," Caplan said. But, he added, "I would still be very prudent about going if you're of reproductive age."

"Why take the risk if you're a fan or tourist?" Caplan asked.

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