Large global gatherings do carry some risk of spreading disease—for example, in 2000 and 2001, the Hajj, the annual Muslim pilgrimage to Mecca, was associated with an outbreak of meningococcus. The CDC has a whole webpage on advice for staying healthy during “mass gatherings.” But it’s still hard to predict the impact of any one gathering affected by any one disease.
And Zika may have already had another, similar opportunity two years ago. Contrary to a popular theory that the virus arrived in Brazil during the 2014 World Cup, a paper published earlier this year in Science estimated a 2013 arrival date for Zika by tracking genome mutations and using epidemiological data. In that case, Zika was already around for one big global event in Brazil. Whether the World Cup played a role in spreading Zika is unclear, but “there’s been a lot of opportunity for Zika to get brought over from Brazil already,” says Messina, who has worked on global risk maps of Zika.
But Arthur Caplan, one of the four authors of the letter, and a professor of bioethics at New York University, thinks the nature of the Olympics makes them deserve special consideration. “Others have said there’s tons of travel going on there anyway, but it’s not coming from every nation in the world,” he says. “I don’t think there’s any event that brings the whole world together like the Olympics.”
It might be safer if the people of the world just stayed a little more apart. Or it might be fine. It will be winter in Brazil in August, so the weather won’t be quite as mosquito-friendly. On the other hand, a recent report from Reuters says Rio still has a lot of sewage it hasn’t cleaned up, which, when it comes to mosquito control “doesn’t inspire me,” Caplan says.
It’s just a very uncertain situation, and uncertainty is pretty much Zika’s calling card. “Most of what we thought we knew turned out to be mistaken,” says Stephen Morse, a professor of epidemiology at Columbia University, referring to Zika’s neurological surprises and the fact that it can be transmitted sexually, neither of which were known before this outbreak. “The great uncertainty that we all feel about this is really underlying a lot of this decision—the arguments about moving or [postponing] the Olympics are largely based on the perception of risk.”
The WHO doesn’t seem to think the Olympics are a bigger risk than regular international travel. “The problem is not the Olympics, the problem is other travel besides the Olympics, if there is a problem," David Heymann, the chair of the WHO’s panel of independent experts on Zika told Reuters recently. “So it's just a false security to say that you'll postpone the Olympics and postpone the globalization of this disease.”
“It seems like trying to scare people a little bit,” Messina adds.
Quick-spreading emerging diseases are becoming a regular reality in this globalized world, and it’s true that a once-every-two-years event probably has only a small role to play in that. And it would be downright gobsmacking if the Olympics were actually delayed over Zika. “Personally, do I think they’re gong to postpone or move it? No,” Caplan says.