WHO Clarifies Comments on Asymptomatic Transmission of SARS-CoV-2

Jeff Craven

June 10, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Maria Van Kerkhove, PhD, WHO's COVID-19 technical lead and an infectious disease epidemiologist, caused a stir June 8 when she said that countries are reporting that many of their asymptomatic cases develop into cases of mild disease. For patients with truly asymptomatic disease, countries are "not finding secondary transmission onward. It's very rare," she said.

Suppressing symptomatic cases, on the other hand, would result in a "drastic reduction" in transmission, she noted. "But from the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual," she said.

But on June 9 – following a day of confusion and criticism – Dr. Van Kerkhove sought to clarify her comments on asymptomatic transmission during a live social media Q&A. She noted that while "the majority of transmission that we know about" is through individuals with symptoms, "there are a subset of people who don't develop symptoms, and to truly understand how many people don't have symptoms – we don't actually have that answer yet."

Between 6% and 41% of individuals may be asymptomatic based on estimates, she acknowledged."What we need to better understand is how many of the people in the population don't have symptoms, and separately, how many of those individuals go on to transmit to others," she said.

Dr. Van Kerkhove also emphasized that her initial comments were made in response to a question raised at the press conference, and called it a misunderstanding. "I wasn't stating a policy of WHO or anything like that," she said. "I was just trying to articulate what we know."

The phrase "very rare" referred to a subset of studies and reports WHO had received from its member states following asymptomatic individuals with COVID-19. "I was referring to some detailed investigations, cluster investigations, case contact tracing, where we had reports from member states saying that, when we follow asymptomatic cases, it's very rare – and I used the phrase very rare – that we found a secondary transmission," she said.

Dr. Van Kerkhove's initial comments drew criticism from medical and public health professionals, who said the statement was "confusing" and communicated poorly.

Eric J. Topol, MD, tweeted that WHO had "engendered considerable confusion" with the comments about asymptomatic individuals rarely transmitting SARS-CoV-2. Dr. Topol, the author of a recent analysis published in Annals of Internal Medicine that suggested as many as 40%-45% of COVID-19 cases may be asymptomatic, said that it was not possible to determine whether asymptomatic individuals in the cohorts he studied were capable of spread like pre-symptomatic individuals. "We only know the viral loads are similar from multiple reports. And we do know some spread occurs from [asymptomatic] people," he said.

Andy Slavitt, former acting administrator of the Centers for Medicare and Medicaid Services, said in a tweet that he believed WHO made "an irresponsible statement even though it was based on legitimate observations." Reports by Member States do not reach a "bar of rigor," he said.

Natalie E. Dean, PhD, assistant professor of biostatistics at the University of Florida, tweeted that the initial comments by the WHO seemed to be trying to draw a distinction between asymptomatic individuals who never develop symptoms, and presymptomatic individuals who present as asymptomatic, but later develop symptoms. Finding that asymptomatic cases rarely transmit the virus could change how people exposed to those asymptomatic individuals are monitored, but "it seems more of scientific than practical interest," she noted. "People without current symptoms could be infectious. Act accordingly."

Anthony S. Fauci, MD, director of the National Institute of Allergy and Infectious Diseases, also weighed in on the controversial WHO comments, telling Good Morning America on June 10 that Dr. Van Kerkhove's initial statement that asymptomatic SARS-CoV-2 transmission is a rare event is "not correct."

This story originally appeared on MDedge.com.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.