WHO Clarifies Comments On Asymptomatic Transmission Of Coronavirus

The organization says it isn’t sure how often people who are infected with the coronavirus but lack symptoms spread it to others. WHO Clarifies Comments On Asymptomatic Transmission Of Coronavirus

The World Health Organization said Tuesday it isn’t clear how often people contract and then spread Covid-19 without showing symptoms, pulling back from a top official’s earlier assertion that such invisible transmission appears rare.

The clarification suggests that, six months into the coronavirus pandemic, the United Nations agency and researchers lack clarity on what is a central riddle in how the respiratory disease circulates. Estimates suggest at least 6%—and as much as 41%—of people who contract the disease don’t have symptoms, said WHO Technical Lead Maria Van Kerkhove. There is no medical consensus on how many of those individuals then infect somebody else.

“That’s a big open question and that remains an open question,” she told reporters. “It’s a new disease. We’re learning a lot about it.”

Her statement followed criticism from public-health researchers of her remarks Monday, when she said, “From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual.”

On Tuesday, she said she had been unclear, while saying her earlier assertion was based on privately-conveyed data from governments she didn’t identify, as well as “two or three studies.”

The confusion underscores how little health experts agree on even basic questions over how coronavirus spreads, with the WHO taking positions that other governments and health authorities argue against.

The agency first discouraged governments in Europe and the U.S. from banning travel to and from China, a step authorities now say was critical in buying time to react. In January, the agency gave mixed messages on whether or not evidence pointed to human-to-human transmission.

Concerns that the disease may be spreading from people who don’t appear sick prompted authorities first in Europe and then the U.S. to ask citizens to wear face masks, even if they feel fine. Face masks can block respiratory droplets that fly from the mouth while speaking. The WHO, however, initially recommended only sick people or their caregivers wear a mask, a position it later softened on evidence that some asymptomatic individuals may be spreading the disease to others.

The question of such so-called silent spread is an enormous matter for the global economic recovery, affecting how easily countries can relax lockdown measures or screen for suspected cases. From the early weeks of the pandemic, health experts have suspected that many individuals who don’t feel or look sick may be unwittingly spreading the virus to others.

Other public-health researchers have warned that the WHO was much too optimistic in its reliance on private data from governments—or a handful of studies—to conclude that such asymptomatic spread is rare.

The disease would be easier to contain if only visibly ill people could spread it, allowing businesses and schools to reopen with greater confidence that simple steps like temperature checks could prevent transmission. So-called “silent spread” makes the disease much harder to track, would require people to maintain a safe physical distance from even healthy individuals, and renders steps like airport screenings far less effective.

“I’m absolutely convinced that that is occurring, the question is how much,” Mike Ryan, executive director of WHO’s emergencies program, said Tuesday.

Several modeling studies suggested that as much as 60% of Covid-19 transmissions are from people who haven’t yet, or will never, show symptoms, the Harvard Global Health Institute said in a statement. There is also evidence that individuals may be most infectious in the day or two before they develop symptoms.

“The WHO created confusion yesterday,” the Institute said. “If new evidence becomes available, WHO should be transparent, make all available data publicly accessible and take the time to thoroughly brief the media and the public on the nature and interpretations of the findings.”

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