Why the Olympics Actually Won't Cause Zika to Spread Everywhere

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With the 2016 Olympic Games in Brazil less than a month away, concerns are mounting that the international event may spread the Zika virus to more countries around the world. Indeed, global travel has been contributing to the spread of virus in the Western Hemisphere since at least 2015, according to a new report from the Centers for Disease Control and Prevention (CDC).

However, the new report, released today (July 13), should help quell fears for many countries that do not currently have the Zika virus: The CDC predicted that the Olympics will put only four countries at risk for importing Zika.

However, the agency also recommended that pregnant women in the U.S. avoid traveling to the Olympics. The virus has been linked with severe brain problems, including a condition called microcephaly, in babies born to women infected during pregnancy.

August and September are winter months in the Southern Hemisphere, and so the weather in Rio de Janeiro, Brazil, during the Olympics will be cooler and drier than at other times of the year. This type of weather typically reduces mosquito populations and therefore lowers the risk of infection, the CDC said. [Zika Virus News: Complete Coverage of the 2016 Outbreak]

Between 350,000 and 500,000 people from more than 200 countries are expected to ravel to Rio de Janeiro in August and September for the Olympic and Paralympic Games, according to the Brazilian Tourist Board. However, these estimates represent less than 0.25 percent of the number of travelers who visited Zika-affected countries in 2015, according to the report. More travelers would mean a greater likelihood of spreading Zika.

In the new report, researchers at the CDC looked at the 167 countries where no cases of the Zika virus have been reported. (The United States, where Zika has been documented, was therefore not included in the 167 countries.) The researchers said that 148 of these countries should not be considered at risk for importing Zika from the Olympics, because they do not have populations of the Aedes aegypti mosquito, which carries Zika, in August and September.

Of the 19 remaining countries, the CDC researchers predicted that only four — Chad, Djibouti, Eritrea and Yemen — are at risk for importing the Zika virus because of people traveling to the Olympics and returning home with the virus. The other 15 countries will have too few travelers attending the Olympics for it to be likely they'd bring home the virus, the researchers said. 

The researchers noted that these estimates were based on five "worst-case scenarios." These scenarios assumed that Zika transmission would not decrease during the winter months, that preventive measures to protect against mosquito bites would not be taken, that anyone who was infected with Zika would have symptoms when they returned to their home countries, that people who were infected would return home immediately and that the home countries would not use precautions to prevent mosquito bites in their home countries.

Though the risk of Zika is low, the CDC still encouraged people traveling to Rio de Janeiro to take certain precautions:

  • Pregnant women should not travel to the Olympics.
  • Travelers should take protective measures to prevent mosquito bites (such as using insect repellent and wearing long-sleeved shirts and long pants) while at the Olympics, and for three weeks after returning to their home countries.
  • To prevent sexual transmission of Zika, travelers should use condoms or abstain from sex. Males in particular should use condoms for eight weeks after travel, or, if they do get Zika, for six months from the start of symptoms.
  • Males who travel to the Olympics and who have pregnant partners should use condoms or abstain from sex for the duration of their partners' pregnancies.
  • Couples who travel to the Olympics and want to get pregnant afterward should wait at least eight weeks, or six months if the male partner has a symptomatic Zika infection.

Originally published on Live Science.

Sara G. Miller
Staff Writer
Sara is a staff writer for Live Science, covering health. She grew up outside of Philadelphia and studied biology at Hamilton College in upstate New York. When she's not writing, she can be found at the library, checking out a big stack of books.