Senator Jeanne Shaheen (D-N.H.) cited Attaran's commentary in a May 17 letter urging the World Health Organization (WHO) to evaluate the risks of holding the Olympics this year. “All of the efforts underway to prevent Zika are at risk of being undone if the Olympic Games spurs a global outbreak,” she wrote.

For Brazil, however, the postponement or cancellation of the Olympics may further destabilize the troubled nation. The country is in its deepest recession on record and consumed by a political crisis with the impeachment trial of President Dilma Rousseff. It is spending almost $10 billion to host the first Olympic Games in South America, money it can ill afford to waste. This is especially the case because it's unlikely that insurers would make anyone associated with the games whole over Zika-induced cancellation claims.

Low risk

Attaran and Caplan may be in the minority among public health experts, as many agree that putting off the games because of Zika is a step too far. The evidence available so far suggests that “risk of exposure to Zika virus and subsequent adverse health outcomes will be low, in a relatively low-risk part of Brazil at a low-risk time of year,” according to a May 10 editorial in the journal Lancet Infectious Diseases. The virus is concentrated in Brazil's northeast, not in Rio, and Olympic sites will be targeted for mosquito control with spraying and elimination of standing water, the journal wrote.

The U.S. Centers for Disease Control and the WHO have advised pregnant women not to travel to areas where Zika is circulating. After Attaran's article appeared, a statement from the WHO reiterated that advice. Other visitors should take steps to avoid being bitten and should use condoms or abstain from sex because men can transmit Zika to sex partners. “The games will take place during Brazil's wintertime, when there are fewer active mosquitoes and the risk of being bitten is lower,” the WHO noted.

In an e-mail, a spokesman for the International Olympic Committee said only that it is following the WHO's guidance and working to minimize any risk to visitors.

Zika's health burden is hard to ascertain

There have been more than 1,300 cases of microcephaly “potentially associated” with Zika, almost all in Brazil, according to the WHO. The true extent of Zika's health burden is hard to ascertain, because cases may go unreported, and months may pass before a woman infected during pregnancy gives birth. No one can say for sure what the risk of Zika in Rio will be three months from now.

Attaran contends that cases of dengue, a virus transmitted by the same mosquitoes, are unexpectedly high in Rio this year, and Zika may not wane in the southern hemisphere's winter, as expected. If even a few travelers introduce the virus to new countries, he warned, the result would be “a full-blown global health disaster.”

If the threat is as grave as his language implies, is there a case for shutting down travel more broadly? Perhaps, but the spread of Zika in this fashion has been underway for some time. “There are lots of people getting off airplanes today in Zika-infected countries,” said William Schaffner, a professor of infectious diseases and preventive medicine at Vanderbilt University in Nashville, Tenn. “We've had several hundred introductions of Zika into the U.S. already.”

Put in perspective, the Olympics won't present a massive increase in visitors to Brazil compared with its regular tourism and travel numbers. The games are expected to bring from 350,000 to 500,000 foreign visitors to Rio, while Brazil had 6.4 million foreign visitors in 2014, and Brazilians made 9 million trips abroad. Attaran said much of that travel, however, was within the region where Zika has already spread, while the Olympics will bring people from all over the planet. He said the question of broader restrictions ”needs further study. I think that case could exist.”

Economic damage

In past infectious outbreaks such as the SARS scare in 2003, most of the economic damage came not from the disease itself but from the attendant disruption to commerce and travel. ”The fact is that the Rio Olympics are going to go forward and no amount of sensationalism will stop it,” Lawrence Gostin, director of the O'Neill Institute for National and Global Health Law at Georgetown Law, wrote in an e-mail. Suspending the games “could bring an already weakened economic and political system to a point of near collapse.”

Gostin conceded that systemic instability may serve to amplify the spread of Zika, noting Brazil's struggles with mosquito control. “What is urgently needed is for the international community, led by the WHO, to declare an all-out war on the mosquito population in Rio. That has not happened,” he wrote. “The failure to do everything possible to control and even eliminate the mosquito population in Rio is a national embarrassment. But more than that, it is an utter international failure.”

Insurance industry covering about $1 billion in potential claims

Though unlikely, if the IOC and Brazil were to seriously consider moving or cancelling the games, they would do so with the knowledge that it might be a total loss. Andrew Duxbury, an underwriting manager in the U.K. branch of Munich Re, said his company is covering about $200 million in potential losses for stakeholders in this summer's games. He estimated that the insurance industry as a whole is covering about $1 billion in potential claims. Most of that exposure is held by a handful of large reinsurers, including Munich Re, Swiss Re, and Hannover Re. If, for instance, a terrorist attack or natural disaster were to prevent all or some of the games, they would cover the losses of organizers, the host nation, TV networks, and other contract holders for money already spent on the event, not to mention lost revenue.

Infectious disease risks usually require separate, additional coverage. Most of the insurance contracts were signed four years ago, and when insurers decide to get reinsurance, as many do for risks this large, that generally happens at the same time as the initial contract. Zika wasn't high on the radar four years ago, so the agreements probably didn't mention it.

Moreover, Zika was first discovered in monkeys in 1947. Since the disease has been known for almost 70 years, it is considered a preexisting condition.