The World Health Organization tried on Tuesday to clear up confusing comments about how often people can spread the coronavirus when they do not have symptoms.
The organization held a live Q&A on its social media pages to address questions about comments made by a WHO official that suggested asymptomatic people only rarely spread Covid-19.
The comments appeared to directly contradict guidance from public health organizations, including the US Centers for Disease Control and Prevention, which have said about a third of coronavirus infections may be asymptomatic.
The CDC also estimates that 40% of coronavirus transmission is occurring before people feel sick, meaning they are presymptomatic.
But it may boil down to how one defines “asymptomatic.”
‘There are so many unknowns’
Maria Van Kerkhove, WHO’s technical lead for coronavirus response and head of its emerging diseases and zoonoses unit, said during a media briefing in Geneva on Monday that “it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual.”
But then on Tuesday, during the live Q&A, she clarified “this is a major unknown.”
“The majority of transmission that we know about is that people who have symptoms transmit the virus to other people through infectious droplets — but 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 answered yet,” Van Kerkhove said.
“We do know that some people who are asymptomatic, or some people who don’t have symptoms, can transmit the virus on,” she said. “So 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.”
On Monday, Van Kerkhove had said that what appear to be asymptomatic cases of Covid-19 often turn out to be cases of mild disease.
Infected people without symptoms might be driving the spread of coronavirus more than we realized
Infected people without symptoms might be driving the spread of coronavirus more than we realized
“When we actually go back and we say how many of them were truly asymptomatic, we find out that many have really mild disease,” Van Kerkhove said on Monday.
“They’re not quote-unquote Covid symptoms — meaning they may not have developed fever yet, they may not have had a significant cough, or they may not have shortness of breath — but some may have mild disease,” Van Kerkhove said. “Having said that, we do know that there can be people who are truly asymptomatic.”
Van Kerkhove added that she was referring to reports from WHO member states when she made her comments on Monday.
“What I was referring to yesterday in the press conference were very few studies — some two or three studies that had been published that actually try to follow asymptomatic cases, so people who are infected, over time, and then look at all of their contacts and see how many additional people were infected,” Van Kerkhove said.
“And that’s a very small subset of studies. So I was responding to a question at the press conference. I wasn’t stating a policy of WHO or anything like that,” she said. “Because this is a major unknown, because there are so many unknowns around this, some modeling groups have tried to estimate what is the proportion of asymptomatic people that may transmit.”
