The World Health Organization has clarified remarks from a press conference on Monday during which the head of the WHO’s emerging diseases and zoonosis unit, Maria Van Kerkhove, said that coronavirus transmission from asymptomatic carriers — a person who does not develop any COVID-19 symptoms — was a “very rare” phenomenon.
“We do know that some people who are asymptomatic, or some people who do not have symptoms, can transmit the virus on,” said Kerkhove, who also explained that she was not “stating a policy of WHO or anything like that” but referencing a subset of studies “that actually try to follow asymptomatic cases.”
“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, later adding that a big open question is how many people are “truly asymptomatic.”
Dr. Isaac Bogoch and Dr. Alan Detsky, professors at the University of Toronto, have previously warned in Forbes that some people who aren’t actually asymptomatic are “commonly mislabeled as asymptomatic in both the medical literature and media.”
For example, some people who are considered asymptomatic may be “presymptomatic,” a term used for people who have not yet developed symptoms, or “subclinical,” a term used for people who don’t develop detectable symptoms or who only develop symptoms too mild to be detected by the healthcare system.
Kerkhove offers a similar caveat, noting “a number” of people who are reported as asymptomatic “may have mild disease” or they “may go onto develop symptoms.”
“We don’t have a clear picture of this,” she said. “We’re six months into a pandemic, there’s a huge amount of research that is being done, but we don’t have that full picture yet.”
Kerkhove also said that some modeling groups have tried estimating the proportion of asymptomatic transmission — which she says offer a “big range,” as high as 40% — “but those are from models so I didn’t include that in my answer yesterday but wanted to make sure that I covered that here.”
The World Health Organization’s remarks on Monday have been a source of widespread confusion, with members of the medical community noting that the global health body’s communication on the issue has been poor.
“Such a statement from the world health organization should be accompanied by data,” said Dr. Ashis Jah, director of the Global Health Institute at Harvard University.
.@WHO communication here not stellar
If folks without symptoms truly “very rarely” spread virus, would be huge.
But such a statement by @WHO should be accompanied by data.
Asymptomatic spread is Achille’s heal of this outbreak
Would love to be wrong. Need to see data
— Ashish K. Jha (@ashishkjha) June 8, 2020
“It’s a mess. I don’t know why they would say asymptomatic transmission is very rare when the truth is we simply don’t know how frequent it is,” Eric Topol, a professor of molecular medicine at Scripps Research, told The Washington Post. “And it doesn’t change the facts we do know, which is that this virus is very transmissible and is very hard to combat.”
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