’A big, open question’: WHO clarifies statement about asymptomatic coronavirus transmission

The World Health Organization said Tuesday that the likelihood of asymptomatic coronavirus carriers to transmit disease was still an open question, tempering remarks made the day before indicating it was rare.

The question hinges on whether people are asymptomatic – that is, infected but without ever exhibiting symptoms – and presymptomatic, which applies to people who have been infected and have not yet manifested illness. The latter are contagious, most experts agree.

The trick is knowing which asymptomatic people will actually turn out to be presymptomatic, WHO scientist Dr. Maria Van Kerkhove, the organization’s technical lead on the coronavirus pandemic, clarified on Tuesday.

“The majority of transmission that we know about is that people who have symptoms transmit the virus to other people through infectious droplets,” Van Kerkhove said, according to Stat News. “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 answer yet.”

The studies that led Kerkhove to assert that people who never develop illness are not likely to spread the virus were small and based on “detailed contact tracing,” she said, according to BBC News. Clusters involving people in that category indicated that it was “very rare” to find infections among their contacts.

But these studies were quite small, she said, which means that extrapolating globally is still a “big open question,” she said, reported BBC News.

Kerkhove made her follow-up remarks after pushback from the international medical community, amid fears that people will think it means face coverings are not essential to prevent spread.

“Both asymptomatic AND pre-symptomatic spread huge problem for controlling disease because [of] folks shedding virus while asymptomatic,” tweeted Dr. Ashish K. Jha, director of the Harvard Global Health Institute. “Asymptomatic spread is Achilles’ heel of this outbreak.”

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