The W.H.O. walked back an earlier assertion that asymptomatic transmission is ‘very rare.’
A top expert at the World Health Organization on Tuesday walked back her earlier assertion that transmission of the coronavirus by people who do not have symptoms is “very rare.”
Dr. Maria Van Kerkhove, who made the original comment at a W.H.O. briefing on Monday, said that it was based on just two or three studies and that it was a “misunderstanding” to say asymptomatic transmission is rare globally.
“I was just responding to a question, I wasn’t stating a policy of W.H.O. or anything like that,” she said.
Dr. Van Kerkhove said that the estimates of transmission from people without symptoms come primarily from models, which may not provide an accurate representation. “That’s a big open question, and that remains an open question,” she said.
Scientists had sharply criticized the W.H.O. for creating confusion on the issue, given the far-ranging public policy implications. Governments around the world have recommended face masks and social distancing measures because of the risk of asymptomatic transmission.
A range of scientists said Dr. Van Kerkhove’s comments did not reflect the current scientific research.
“All of the best evidence suggests that people without symptoms can and do readily spread SARS-CoV-2, the virus that causes Covid-19,” scientists at the Harvard Global Health Institute said in a statement on Tuesday.
“Communicating preliminary data about key aspects of the coronavirus without much context can have tremendous negative impact on how the public and policymakers respond to the pandemic.”
A widely cited paper published in April suggested that people are most infectious about two days before the onset of symptoms, and estimated that 44 percent of new infections are a result of transmission from people who were not yet showing symptoms.
Dr. Van Kerkhove and other W.H.O. experts reiterated the importance of physical distancing, personal hygiene, testing, tracing, quarantine and isolation in controlling the pandemic.
The U.S. caseload, already the world’s highest, is approaching two million. A book about the fall of France in 1940 has become a hit during the pandemic.
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