WHO has to walk back asymptomatic comments

The World Health Organization moved Tuesday to clarify its position on whether people without symptoms are widely spreading the new coronavirus, saying much remains unknown about asymptomatic transmission.

A comment by a WHO official Monday — calling such asymptomatic transmissions “very rare” — touched off a furious scientific debate over the unresolved question and attracted widespread criticism of the organization.

Less than 24 hours later, the WHO convened a news conference to walk back its comments, stressing much remains unknown. But the comment from Monday had already spread widely.

The episode sparked criticism of the WHO’s public health messaging and highlighted just how fraught and easily politicized such work remains months into the pandemic.

Calling the controversy “a misunderstanding,” Maria Van Kerkhove, head of the WHO’s emerging disease and zoonosis unit, said during the news conference Monday, she was trying to respond to a journalist’s question when she said asymptomatic transmission was “very rare.”

“I wasn’t stating a policy of WHO or anything like that,” she said. “We do know that some people who are asymptomatic, or some people who do not have symptoms, can transmit the virus on.”

It was not the “intent of WHO to say there is a new or different policy,” added Mike Ryan, head of emergency programs for the WHO. “There is still too much unknown about this virus and still too much unknown about its transmission dynamics.”

While asymptomatic transmission does occur, no one knows how frequently it happens. Studies and models have suggested many of those infected never show symptoms. And it remains an open question whether they are a large force driving transmission. Some countries using contact tracing to work backward from confirmed cases have not found many instances of asymptomatic spread, WHO officials noted.

At the same time, WHO officials acknowledged Tuesday some modeling studies have suggested as much as 41% of transmission may be due to asymptomatic people.

“It’s a mess. I don’t know why they would say asymptomatic transmission is very rare when the truth is we simply don’t know how frequent it is,” said Eric Topol, a professor of molecular medicine at Scripps Research.