The World Health Organization kept the Zika outbreak and its neurological complications under a global public-health emergency this week, but concluded that the Rio de Janeiro Olympics would pose a “very low” additional risk of spreading the virus internationally.

The judgment, issued Tuesday after the third meeting of WHO’s emergency committee, attempts to separate two questions that have become increasingly entangled: whether Zika remains a grave threat to pregnant women and developing fetuses, and whether moving or canceling a mass sporting event would materially slow an epidemic already established across much of the Americas.

The committee’s formal statement answered both questions firmly. The association between Zika infection, microcephaly and Guillain-Barré syndrome still warrants the emergency designation. But international travel to Brazil is already extensive, transmission in Rio is expected to be lower during the Southern Hemisphere winter, and the Games are unlikely to alter the virus’s global course.

An emergency defined by complications, not ordinary symptoms

Zika infection is often mild or produces no symptoms, which makes surveillance difficult. The emergency arises from mounting evidence that infection during pregnancy can cause microcephaly and other severe fetal brain abnormalities, and that infection can be associated with Guillain-Barré syndrome, a disorder in which the immune system attacks peripheral nerves.

WHO’s June 16 situation report said no new country had reported mosquito-borne or person-to-person transmission in the preceding week, but the geographic scope remained broad. The report reiterated the scientific consensus that Zika is a cause of microcephaly and Guillain-Barré syndrome and said the associated disorders continued to meet the definition of a Public Health Emergency of International Concern.

That framing matters because it directs resources toward pregnancy surveillance, diagnostic capacity, mosquito control and research rather than toward the mild febrile illness alone. There is no vaccine, no specific treatment and no widely available test simple enough to resolve every suspected infection. Many cases escape detection, and laboratory interpretation can be complicated by cross-reaction with related flaviviruses such as dengue.

Why the Olympics do not change the global equation

More than 200 academics had urged WHO to reconsider the Games, arguing that hundreds of thousands of visitors could carry infection home to places where Aedes mosquitoes are present. The committee reviewed those concerns but found no public-health justification for postponing, canceling or relocating the Olympics or Paralympics.

WHO’s earlier travel advice for the Games notes that Brazil is only one of almost 60 countries and territories reporting ongoing mosquito transmission. Regular movement among those places is far greater than the temporary flow expected for the Games. Rio’s cooler and drier August weather should also suppress mosquito activity, though it will not eliminate individual risk.

Modeling cited before the committee meeting projected a small number of infections among foreign visitors. Reuters reported that one São Paulo group estimated no more than 15 infections among visitors. Such projections depend on assumptions about attendance, mosquito density and the underlying rate of infection, but they illustrate why the committee distinguished the visibility of the Olympics from its epidemiological contribution.

The conclusion is not an all-clear. Pregnant women are advised not to travel to areas with ongoing Zika transmission, including Rio. Travelers should use insect repellent, wear clothing that limits exposed skin, stay in screened or air-conditioned accommodations and take precautions against sexual transmission. WHO also advised Brazilian authorities to intensify mosquito control around venues and visitor areas.

Personal risk remains sharply unequal

For most travelers, Zika is likely to cause no symptoms or a short illness marked by rash, fever, joint pain or conjunctivitis. For a pregnant traveler—or the pregnant partner of an infected traveler—the consequences may be profound. That asymmetry explains why a “very low” contribution to worldwide spread can coexist with strong advice against travel for a specific group.

The Centers for Disease Control and Prevention’s Olympics guidance recommends that pregnant women consider not attending and that travelers take mosquito and sexual-transmission precautions. The advice reflects evidence that Zika can persist in semen longer than in blood, creating a pathway of transmission after a traveler has returned home.

Research from Colombia underscores the scale and uncertainty. A study published in the New England Journal of Medicine reported tens of thousands of suspected infections, including nearly 12,000 among pregnant women, while noting that pregnancy outcomes and timing of infection required continued follow-up. The absence of detected abnormalities in many late-pregnancy infections did not resolve the risk from earlier exposure.

Public-health credibility depends on explaining the distinction

WHO’s task is complicated by criticism of its emergency responses and by the intense attention attached to a global sporting event. A conclusion that the Games should proceed can sound dismissive if communicated without the accompanying warnings. The emergency committee therefore maintained the highest international alarm while declining to recommend a measure it judged epidemiologically ineffective.

Independent infectious-disease analysis reached a similar reading of the decision. The University of Minnesota’s Center for Infectious Disease Research and Policy reported Tuesday that the committee saw no basis for general travel or trade restrictions, while preserving special guidance for pregnant women and emphasizing surveillance in returning travelers.

The tension is visible in the scientific debate. A contemporaneous analysis in Wired argued that winter conditions and the small fraction of global travel represented by the Games support WHO’s conclusion; critics counter that even a small number of exported infections may matter where competent mosquitoes and susceptible populations overlap.

For health systems, the operational priorities are less ambiguous. Clinicians must ask pregnant patients and their partners about travel, public laboratories need capacity for complex testing, blood services must reduce transfusion risk, and local authorities must prepare for mosquito-borne transmission. Research must clarify how often infection causes fetal injury, how long sexual transmission remains possible and which interventions work.

The Olympics have become the most visible symbol of the Zika crisis, but WHO’s decision rests on a broader map. The virus is already moving through routine travel, mosquitoes and sexual contact across scores of countries. Preventing congenital injury will depend less on changing one event than on sustained surveillance, candid risk communication and protection targeted to the people for whom infection carries its highest stakes.