This story originally appeared on Time.com.
Scientists including Marques argue that large events like the Olympics or the World Cup often take place in areas with high rates of mosquito-borne illness, and that not enough attention is paid to the fact that, while these are summer Olympics, they will actually take place during Brazil’s winter. The other reason they offer not to be alarmed is an admittedly bleak one: There’s a chance so many people in Brazil will be infected by the time the Games kickoff that the likelihood of spread will be somewhat diminished, since people develop immunity after getting infected. Not everyone agrees with that possibility, but Brazil estimates about 1.5 million people already have the virus.
Still, the Zika virus is scary, and is causing severe and devastating birth defects in thousands of babies. There is also so much scientists still do not know about the virus, such as why some infected pregnant women have infants with the birth defect microcephaly and others do not. But some experts are skeptical about whether the 500,000 people attending the Games will significantly increase the spread of the virus worldwide—especially since close to 50 countries already have active transmission.
The 2016 Olympics in Rio are around the corner, and doctors and athletes alike are skittish about the Zika outbreak, which has pummeled Brazil more than any other country. Recently, more than 220 physicians and scientists signed a petition arguing that the Games should be postponed or moved to another location. But other infectious disease experts tell TIME that the panic from their peers is not based in science.
“The whole issue regarding the Olympics and Zika is very silly,” said Dr. Ernesto Marques of the University of Pittsburgh Center for Vaccine Research and Graduate School of Public Health, who is conducting Zika research in Brazil. “The petition you mention is so naïve and infantile that it does not deserve any comment.”
“I think the reason there is a confusion is there are multiple aspects to Zika, and people are going to a place where there is active transmission,” said Dr. Anthony Fauci, who heads the National Institute of Allergy and Infectious Diseases at the National Institutes of Health. “Pregnant women absolutely should not go to the Olympics,” he added. Their partners may not want to go either, since the virus can spread sexually, and anyone who wants to get pregnant in the next six months may want to sit the Games out as well.
But Fauci said the number of people traveling from the United States to countries where there is active transmission is already so high. “You have millions on millions of people traveling to those places,” Fauci said. “What kind of increment will the Olympics have on a phenomenon that’s already happening?”
The fact that so much remains unknown about the virus will likely keep people on edge. Some journalists are not attending the Games due to pregnancies, and Olympic long jumper Greg Rutherford is reportedly freezing his sperm. For some people, serious precautions may need to be taken. “You have to take Zika seriously and have to protect yourself there and even when you return to your own country so a mosquito doesn’t bite you and infect someone else,” Fauci said. “But when you put all the data together, is that reason to cancel? We are in agreement that that is not good enough reason to cancel the Olympics.”
Some researchers estimate that the risk of Zika spreading at the Olympics will be quite low. A Sao Paulo research group put the number of Zika infections among foreigners at only 15, Reuters reports, which is close to the 16 cases estimated in another April study published in the journal Epidemiology & Infection. Prior research looking at the risk of dengue spread during the 2014 FIFA World Cup in Brazil, when the country was hosting 600,000 foreigners, estimated up to 59 cases of dengue among visitors. In actuality, there were only three cases of tourists infected with dengue during that World Cup. The low numbers are largely due to the weather and the fact the locations where foreigners typically go during the games have high levels of mosquito control.
In another June 2016 paper published in the medical journal Memorias Do Instituto Oswaldo Cruz, Brazilian researchers argued that most of the Zika spread from Brazil to other countries likely already occurred when the country hosted Carnival in February; one million tourists (double the number of people expected for the Olympics) visited Rio de Janeiro then. Not only was the spread of Zika at its peak, but “most Carnival activities took place outdoors, increasing the exposure of tourists to mosquitoes,” the study authors wrote.
People can keep themselves protected from mosquito bites by wearing long clothing, using insect repellant, and making sure there are not pools of water around them where mosquitoes like to breed.