WHO sparks fresh debate
Silent spreader comment downplayed
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.
“It still appears to be rare that an asymptomatic person actually transmits onward to a secondary individual,” Maria Van Kerkhove, head of WHO’S emerging diseases and zoonosis unit, said at a briefing in Geneva. She said her comment, which reiterates the group’s previous position on socalled asymptomatic cases, was based on detailed reports of contact tracing from various countries.
Although the health organization had said as far back as February that it did not see asymptomatic cases as a major cause of viral spread, Van Kerkhove’s remark at a press conference Monday revived controversy over coronavirus transmission routes.
Some of the confusion lies in the distinction between the roles played by truly asymptomatic people and those who are merely pre-symptomatic — and later go on to become ill — in spreading the disease.
“Comprehensive studies on transmission from asymptomatic individuals are difficult to conduct, but the available evidence from contact tracing reported by member states suggests that asymptomatically infected individuals are much less likely to transmit the virus than those who develop symptoms,” the WHO said in guidance on the use of face masks that it issued last week.
Van Kerkhove downplayed her comments Tuesday in a live event on social media, saying that she was referring to some unpublished data and two or three published studies that followed people with coronavirus who never developed symptoms, and tried to determine how many additional people they infected.
“That’s a very small subset of studies,” said Van Kerkhove. “I used the phrase ‘very rare’ and I think that’s a misunderstanding to state asymptomatic transmission globally is very rare.”