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WHO seeks to clarify widely criticized statement on asymptomatic spread

The World Health Organization (WHO) on Tuesday sought to clarify a controversial statement that asymptomatic spread of coronavirus is "very rare," saying instead that much is unknown and some models find that it is not actually rare.

Maria Van Kerkhove, the WHO technical lead for coronavirus, said in a Tuesday Facebook Live video to clarify her earlier statement that there had been "misunderstandings."

Van Kerkhove noted Tuesday that asymptomatic people can in fact spread the virus, though she said it is not known how common that is. "We do know that some people who are asymptomatic or some people who don't have symptoms can transmit the virus on," she said.

She said she was relying on "two or three studies" as well as unpublished reports from some countries to the WHO for her statement, and indicated that "very rare" is perhaps not the best phrase to use.

"In that I used the phrase 'very rare,' and I think that's misunderstanding to state that asymptomatic transmission globally is very rare," she said. "What I was referring to is a subset of studies."

She said that some models show that as much as 40 percent of transmission of the virus could be from asymptomatic people, which would be far from very rare, though those are just estimates from modeling.

"Some estimates of around 40 percent of transmission may be due to asymptomatic, but those are from models, and so I didn't include that in my answer yesterday but wanted to make sure that I covered that here," she said.

Van Kerkhove's answer on Monday had provoked a flurry of criticism and worry from public health experts on Twitter who worried that the WHO was giving the public the wrong impression. Experts said that people should not assume that if they do not have symptoms they cannot transmit the virus.

Another distinction Van Kerkhove made in clarifying Tuesday is that she was referring to truly asymptomatic people, and not people who are presymptomatic, meaning they do not have symptoms at the moment but will later.

Presymptomatic people and those with mild illness that someone might not even notice can transmit the virus, meaning that someone should not assume the absence of symptoms means they are not infectious.

"People who are not showing symptoms can still spread the disease; it's just that they're likely pre-symptomatic rather than truly asymptomatic," tweeted Jeremy Konyndyk, senior policy fellow at the Center for Global Development. "Keep wearing those masks. Keep distancing."

Other experts were frustrated at what they called botched communication from the WHO.

"This is such a mistake that I’m not sure how or if WHO pronouncements can be covered now," tweeted Andy Slavitt, a former top health official in the Obama administration.