The World Health Organization says the spread of coronavirus from people with no symptoms is "rare," following warnings from various experts around the world that such transmission is more common.
Citing data obtained by the WHO, Van Kerkhove said there is spread between asymptomatic and pre-symptomatic people. Still, he suggested concentrating on tracking and isolating symptomatic individuals to help combat the outbreak.
"From the data we have, it still seems to be rare that an asymptomatic person transmits onward to [another] individual," Van Kerkhove said on Monday.
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What exactly does it mean to be asymptomatic?
If you're still asymptomatic, that means you're sick with a virus, but you're never showing signs of illness. Those typical symptoms in the case of coronavirus will be dry cough, fever, and fatigue.
However, people with asymptomatic COVID-19 disease can be contagious as health officials have repeatedly stressed to follow strict social-distancing measures.
The WHO has said this is rarer than commonly thought, but it can happen in nursing homes and household settings.
While the comments drew questions from Twitter experts, this may simply be a matter of semantics. Various experts previously pointed out the misuse of the term "asymptomatic" when referring to "pre-symptomatic" patients.
Dr. Ashish K. Jha, director of the Harvard Global Health Institute, tweeted the distinction and noted that the agency "should be clearer in communication." The official also said that "some models" suggest 40 percent to 60% of the spread is from people who have no symptoms.
How many people with the coronavirus are asymptomatic?
Some studies report alarmingly high numbers. In early April, one laboratory in Iceland said that as many as 50% of cases could be asymptomatic. In the same month, the top medical research body in India reported that 80 of the 100 people they studied had no symptoms. In one homeless shelter in Boston, where 400 guests stayed in April, 146 positively tested for COVID-19, all of which were reported asymptomatic. According to Reuters, at least half of the newly discovered cases of coronavirus in Singapore show no symptoms.
What do health officials say, then? CDC estimated that at least 25% of people with coronavirus could be asymptomatic. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, reported that 25 to 50% of cases may be asymptomatic.
Is it possible that some people who were asymptomatic when they were tested later showed symptoms?
Absolutely. Van Kerkhove told ProPublica she believes many cases were wrongly classified as asymptomatic when they were pre-symptomatic. Pre-symptomatic people do not have symptoms when testing positive, but then develop symptoms.
Some examples of this have been documented. For example, the CDC discovered that of the 13 patients in a Washington State nursing facility who did not show any symptoms after testing positive for coronavirus, then later developed symptoms. It is also possible that some people who have been tested have their own symptoms underplayed.
"Most of the people who were thought to be asymptomatic aren't truly asymptomatic," said Van Kerkhove.
"When [WHO] went back and interviewed them, most of them said [the patients] didn't feel well but didn't think it was an important thing [for them] to mention," she added.
Dr. Jeffrey Shaman, an expert on infectious diseases at Columbia University, cautioned against wasting too much time on the asymptomatic-presymptomatic theoretical controversy.
"The bottom line is that there are people out there shedding the virus who don't know that they're infected," he told the New York Times.
