The World Health Organization’s technical lead for coronavirus response, Maria Van Kerkhove, said at a press briefing on Monday (June 8) that asymptomatic transmission of the SARS-CoV-2 virus was “very rare.” On Tuesday, Van Kerkhove clarified at a follow-up Q&A session on COVID-19 transmission that she was referring only to patients who never show any symptoms at all, not those who have not yet begun to show symptoms—individuals who are classified as being presymptomatic—nor those cases that involve only mild symptoms. The WHO estimates that among truly asymptomatic patients, 16 percent can infect others. “We do know that some people who are asymptomatic can transmit the virus on,” Van Kerkhov said on Tuesday.
Still, many researchers, including National Institute of Allergy and Infectious Diseases Director Anthony Fauci, have challenged the WHO’s assertion that the virus is only rarely spread by truly asymptomatic individuals. “[This] is not backed up by any data,” Fauci tells Science News. “We know that there is asymptomatic transmission. . . . What we do not know is the extent to which that occurs. So when we hear statements that this is very rare, we do not know that as a fact.”
Research on asymptomatic spread has yielded mixed results, and it’s still not even clear what proportion of people infected with SARS-CoV-2 will remain symptom-free. While some studies estimate that fewer than 20 percent of cases are asymptomatic, one review published last week (June 3) in the Annals of Internal Medicine stated it may be as high as 45 percent, and noted that these individuals “can transmit the virus to others for an extended period.”
“What we need to better understand is how many people in the population don’t have symptoms,” Van Kerkhove said on Tuesday. “And, separately, how many of those individuals go on to transmit [the virus] to others.”
She emphasized that the information she’d shared on the previous day was based on a handful of studies that had tracked spread among known asymptomatic cases, and stated that she had not intended to imply that “asymptomatic transmission globally” was uncommon. The WHO said it regrets the statement that transmission by asymptomatic individuals is “very rare,” Axios reports.
The scientific community questioned whether the clarifications from the WHO were enough to overcome the initial misinformation. Given the uncertainty surrounding the issue, the way the WHO’s comments were initially interpreted by the public and covered by the media was “a disaster public relations–wise,” Marm Kilpatrick, an infectious diseases researcher at the University of California, Santa Cruz, tells Science News. “We’ve been trying to get 7 billion people on the planet to wear masks even though they [feel] fine, so to misinterpret [data] like that is super counterproductive.”
Lawrence Gostin, director of the O’Neill Institute for National and Global Health Law at Georgetown University, tells BuzzFeed News, “WHO is tarnishing its reputation as a science agency by putting out conflicting and confusing statements.”
“On the one hand, I do want to cut the W.H.O. some slack, because it is hard to do this in an evolving pandemic,” Ashish Jha, director of Harvard University’s Global Health Institute, tells The New York Times. “At the same time, we do rely on the W.H.O. to give us the best scientific data and evidence.” In a statement on Tuesday, Jha’s institute wrote, “All of the best evidence suggests that people without symptoms can and do readily spread SARS-CoV-2,” STAT reports.