An official with the World Health Organization said on Monday (June 8) that it is very rare for an asymptomatic carrier of coronavirus to spread COVID-19 to others. When the coronavirus outbreak first began, health officials were worried because they found evidence that people did not know they had the virus and were unwittingly spreading it to others.
Now, as researchers have been analyzing contact tracing data, they found that the virus is unlikely to be spread by asymptomatic individuals.
“From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual,” Dr. Maria Van Kerkhove, head of WHO’s emerging diseases and zoonosis unit, said at a news briefing. “It’s very rare.”
Kerkhove said that people without symptoms can still spread the virus and that officials are trying to determine how often it happens.
“I did not say that asymptomatic cases cannot transmit; they can,” Van Kerkhove told TIME. “The question is, do they? And if they do, how often is that happening?”
She explained that one concern is that some people may have mild symptoms, or ones not commonly associated with COVID-19, such as muscle aches and fatigue, and may not realize they have contracted the coronavirus. That makes it difficult for contact traces to know if a person was truly asymptomatic while they were spreading the virus.
“We’re not ruling anything out,” Van Kerkhove said. “We’re not saying that [asymptomatic spread is] not happening. But we’re saying more transmission is happening among symptomatic individuals. People are looking for a binary, and it’s not that.”
The following day Van Kerkhove clarified her comments and said more research needs to be done.
"What I was referring to yesterday in the press conference were very few studies who tried to look at asymptomatic cases over time. … 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 said. "Because this is a major unknown, because there are so many unknowns around this, some modeling groups had tried to estimate what is the proportion of asymptomatic people who may transmit."
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