WHO says 'there's much unknown' about asymptomatic cases after an official suggested they're 'rare'

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(CNN) - The World Health Organization today addressed confusion surrounding an official's comments on Monday suggesting the spread of Covid-19 by asymptomatic people "appears to be rare."

Maria Van Kerkhove, WHO's technical lead for coronavirus response and head of its emerging diseases and zoonoses unit, said yesterday that "it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual."

But then today, during the live Q&A, she clarified that "this is a major unknown."

"We do know that some people who are asymptomatic or some people who do not have symptoms can transmit the virus on — so what we need to better understand is how many people in the population don’t have symptoms," Van Kerkhove said.

She explained further:

"What I was referring to yesterday in the press conference were very few studies who tried to look at asymptomatic cases over time. … And that’s a very small subset of studies, and so I was responding to a question at the press conference. I wasn’t stating a policy," Van Kerkhove said. "Because this is a major unknown, because there are so many unknowns around this, some modeling groups had tried to estimate what is the proportion of asymptomatic people who may transmit."

Dr. Mike Ryan, executive director of the WHO Health Emergencies Programme, also said during the live Q&A that there is still much to learn about the possible asymptomatic spread of the coronavirus.

"Whatever proportion of disease is transmitting from asymptomatic individuals, as Maria said, that is unknown," Ryan said. "There’s much to be answered about this, there’s much unknown."

Ryan added that the virus, a pathogen that is present in the upper respiratory tract, transmits through droplets — such as when someone coughs or sneezes, but some research also suggests it can spread through speaking as well.

Previously, on Monday, Van Kerkhove said that what appear to be asymptomatic cases of Covid-19 often turn out to be cases of mild disease.

"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.

A truly asymptomatic person does not have symptoms and does not go on to develop symptoms of Covid-19. Whereas, the term paucisymptomatic refers to having atypical or very mild symptoms and pre-symptomatic refers to the early stages of an illness, before symptoms have developed.

The US Centers for Disease Control and Prevention estimates in planning scenarios that 40% of coronavirus transmission is occurring before people feel sick.

This story was first published on CNN.com, "WHO says "there's much unknown" about asymptomatic cases after an official suggested they're "rare""