World Health Organization backtracks on asymptomatic coronavirus spread, says much is still unknown

Friday, 12 Jun, 2020

A World Health Organization official's comment that transmission of the novel coronavirus by people who don't develop symptoms is rare sparked a new debate among infectious-disease experts about the risks of so-called silent spreaders of Covid-19.

Maria Van Kerkhove, the WHO's technical lead for coronavirus response and head of the emerging diseases and zoonoses unit, said Tuesday that there had been "misunderstandings" and clarified that people without symptoms can spread the virus. "To truly understand how many people don't have symptoms, we don't have that answer yet".

Following an onslaught of confusion expressed from social media, including from doctors, journalists, and epidemiologists, the World Health Organization hosted a livestream on Facebook, Twitter, and LinkedIn, to clarify questions surrounding transmission of the CCP virus, commonly known as the novel coronavirus. Initially, for example, the thinking was that we didn't have to worry about human-to-human spread of the virus, and that masks wouldn't be effective in limiting its spread - two bits of thinking that did not at all hold up over the long term.

"I used the phrase "very rare" and I think that's a misunderstanding to state asymptomatic transmission globally is very rare".

Detailed studies and testing of people who test positive for the coronavirus but show no symptoms are needed to determine if they spread the disease, and few have been done so far.

Looking at investigations of clusters of infections from various countries, she said that where an asymptomatic case had been followed up it was "very rare" to find secondary infections among their contacts. Let's be clear: Much of #COVID19 transmission is done by people before they show symptoms (i.e. pre-symptomatic, not asymptomatic).

Uncertainty over the issue has hindered nations' efforts to reopen battered economies, with the New England Journal of Medicine previously warning that transmission of SARS-CoV-2 by seemingly healthy people is "the Achilles' heel of Covid-19 pandemic control".

"I continue to believe that, based on the advice that we're getting from the health experts here, that people who are asymptomatic who become symptomatic are absolutely capable of spreading the infection and so are numerous asymptomatic people who never show any symptoms at all", Baker said.

"In fact, the evidence we have given the percentage of people, which is about 25% (to) 45%, of the totality of infected people likely are without symptoms", Fauci said on GMA.

He urged people to follow the advice and feedback of public health officials who questioned Van Kerkhove's initial statements.

Pre-symptomatic transmission has "important implications" for track, trace and isolation measures, Professor Javid said. "They're following asymptomatic cases".

"Whether they're fired up or not, that doesn't prevent them from getting the virus", said Bradley Pollock, chairman of the Department of Public Health Sciences at the University of California, Davis.

WHO's top emergencies expert, Dr. Mike Ryan, explained the coronavirus travel in the upper respiratory tract, which allows the virus to transmit droplets. That was why the disease spread so easily, he said.

She emphasized that the information she'd shared on the previous day was based on a handful of studies that had tracked spread among known asymptomatic cases, and stated that she had not meant to imply that "asymptomatic transmission globally" was uncommon. Specifically: people with symptoms, who are in close contact with others and who aren't using personal protective equipment like masks.