Are asymptomatic people spreading the coronavirus? A WHO official’s words spark confusion, debate.

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

In her initial comments, the head of the WHO’s emerging disease and zoonosis unit Dr. Van Kerkhove said: “We have a number of reports from countries who are doing very detailed contact tracing.  They’re following asymptomatic cases.  They’re following contacts.  And they’re not finding secondary transmission onward.  It’s very rare.”  Within minutes, that single stray comment regarding initial reports and experiences from tracers from other countries, was seized upon and amplified by some news outlets as proof that physical distancing, face masks, and safer-at-home orders are unnecessary.  Networks, programs, and hosts with science editors and fact checking resources at their beck and call, preferring not to call upon them, not to responsibly report, but rather politicize a comment that should not have gained such attention or certitude.  

Experts pointed out several problems with the WHO’s initial statement.

“All of the best evidence suggests that people without symptoms can and do readily spread SARS-CoV-2, the virus that causes Covid-19,” the Harvard Global Health Institute said in a statement Tuesday. “In fact, some evidence suggests that people may be most infectious in the days before they become symptomatic.”

An influential study published in April in the journal Nature found evidence that people can be very infectious roughly two days before symptoms appear.  The study estimated 44% of infections are coming from people not yet showing symptoms.

A review published just last week in the Annals of Internal Medicine of 16 of the most relevant studies of asymptomatic infection found a likely rate of 40 to 35% of those infected don’t have symptoms.  But the authors concluded that every study on the subject has been “imperfect in many ways.”  

We don’t really know the contribution of asymptomatic transmission.  Sometimes it is best to say exactly that. (June 11, 2020)