WHO Backtracks On Statement About 'Rare' Asymptomatic Spread of Coronavirus

The World Health Organization (WHO) on Tuesday walked back statements made during a Monday news briefing that suggested asymptomatic spread of the novel coronavirus is uncommon.

During a media event, the WHO's Dr. Maria Van Kerkhove said current estimates indicated anywhere between 6 and 41 percent of the population could have the coronavirus without knowing it, and those people could in turn pass the virus on to others.

"We do know that some people who are asymptomatic, or some people who don't have symptoms, can transmit the virus on," Van Kerkhove said. "What we need to better understand is how many of the people in the population don't have symptoms and, separately, how many of those individuals go on to transmit to others."

People wearing masks in NYC
A woman stands on the Coney Island boardwalk in Brooklyn, New York, on May 25. On Tuesday, the World Health Organization clarified previous statements suggesting that transmission of the coronavirus from infected people without symptoms of COVID-19 was "rare." John Lamparski/Getty

Van Kerkhove appeared during a question and answer session open to the public after statements she made during Monday's news briefing raised confusion about whether asymptomatic patients can spread the virus.

"From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual," Van Kerkhove said Monday.

The implication that asymptomatic people with the virus are not at risk of transmitting it to others contradicted previous WHO warnings and international guidelines on wearing facial coverings, which are intended to prevent the virus's spread from those who have it but are not experiencing symptoms.

The WHO released its most recent guidelines on personal protective equipment last week. It recommended that members of the general public in areas where virus transmission is possible should wear fabric masks when physical distancing cannot be done.

"If you yourself are infected—and you may not know it yet, because there is the possibility of asymptomatic transmission or pre-symptomatic transmission—if you put that fabric mask on, you reduce that opportunity to transmit to someone else," Van Kerkhove said Tuesday.

In addition to confusion about how contagious asymptomatic people with the virus are, Van Kerkhove said there was also widespread misunderstanding about the difference between pre-symptomatic and asymptomatic cases. While some individuals take a few days to develop symptoms after testing positive for the virus—thus representing the pre-symptomatic cases—others never experience any symptoms at all.

"When we say asymptomatic, we mean somebody that does not have symptoms and does not go on to develop symptoms. Truly no symptoms," Van Kerkhove said.

The clarifications came as many countries are beginning to reopen their economies after weeks or months of shutdowns. On Monday, the WHO's director-general, Tedros Adhanom Ghebreyesus, said that while many European countries were showing signs of recovery, "globally it's worsening," with the WHO receiving reports of the largest spike in new cases within the past week.

"More than six months into this pandemic, this is not the time for any country to take its foot off the pedal," Ghebreyesus said.

By Tuesday, the WHO's estimates indicated that more than 7 million cases and more than 404,000 deaths had been reported worldwide.

With new cases still on the rise and many countries reopening, the WHO took steps to address the confusion regarding virus transmission as Van Kerkhove's statements on Monday got criticized by other medical professionals.

"I used the phrase 'very rare,'" Van Kerkhove said of her Monday comments. "I think that's misunderstanding to state that asymptomatic transmission globally is very rare. What I was referring to was a subset of studies," she said, adding that some of the studies she referred to during Monday's news briefing focused specifically on contact tracing of asymptomatic cases.

Since the coronavirus is still so new, Kerkhove said, WHO and health officials around the world still do not know a lot about how it spreads, especially among those who do not exhibit symptoms.

"What we need to understand—and this is one of the major unknowns—is what proportion of that is contributing to transmission," Kerkhove said.

The WHO did not respond to Newsweek's request for comment before publication.