Doctor Says WHO's Statement About Asymptomatic Spread Is Dangerous

On Monday, a World Health Organization (WHO) official announced that asymptomatic coronavirus patients are not contributing significantly to the spread of the virus. "From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual," Maria Van Kerkhove, PhD, who helms the WHO's emerging diseases and zoonosis unit, said at a news briefing. "It's very rare." The statement—particularly, Van Kerkhove's use of the phrase "very rare"—struck many as a major shift away from previous publicized research. WHO has since walked back on its statement a bit, but an infectious disease doctor we spoke with prior to WHO's clarification voiced concern about the statement—and is urging people to proceed with continued caution.

"I am not as confident that spread from asymptomatic or pre-symptomatic individuals is rare," says Thomas Russo, MD, chief of the division of infectious disease at the University at Buffalo. While there is a distinction between asymptomatic patients (those who never develop symptoms) and pre-symptomatic patients (those who are infected but have yet to develop symptoms), Russo says that both of those groups "are functionally equivalent in that both could spread virus when healthy."

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In May, for example, the Centers for Disease Control and Prevention (CDC) estimated that 40 percent of infections were from those without symptoms (including both asymptomatic and pre-symptomatic individuals).

Russo says, "I feel at this point it is much safer to assume this occurs more than rarely to keep people safe." He adds that WHO's statement was "premature" and potentially even dangerous, as it "risks generating a false sense that if you feel well, you are not infectious."

WHO received a ton of feedback after Van Kerkhove's comments, prompting a Tuesday news briefing in which she and Mike Ryan, MPH, executive director of WHO's Health Emergencies Program, somewhat clarified the organization's understanding of asymptomatic spread.

"What I was referring to yesterday in the press conference were very few studies who tried to look at asymptomatic cases over time," Van Kerkhove said, referencing not-yet-published contact tracing data. "And that's a very small subset of studies, and so I was responding to a question at the press conference. I wasn't stating a policy."

Van Kerkhove and Ryan added that both the number of people who are asymptomatic and those who are asymptomatic and transmitting the virus are still a "major unknown." "Whatever proportion of the disease is transmitting from asymptomatic individuals—and, as Maria said, that is unknown… That is occurring. I'm absolutely convinced that that is occurring," Ryan said. "The question is, how much."

Russo agrees, saying it's not a matter of whether asymptomatic and pre-symptomatic coronavirus patients can spread COVID-19—but to what degree that happens. "We know that you can be asymptomatic/pre-symptomatic and spread infection," Russo says. "The question that is unresolved is what portion of secondary cases are a result of this mode of transmission. I doubt it is rare—but time will tell." And for more insight on why people respond differently to coronavirus, This Is Why Some People Have Coronavirus Symptoms and Others Don't.