The World Health Organization on Tuesday sought to clarify a top official’s claim, made just a day earlier, that asymptomatic transmission of the coronavirus is “very rare,” saying that a significant percentage of transmissions may in fact occur through people who are not experiencing symptoms.
Dr. Maria Van Kerkhove, who leads the WHO’s diseases and zoonosis unit, clarified her earlier remarks, saying that asymptomatic spread remains a “complex question” and that she was referring to a “small subset of studies.”
“I was responding to a question at the press conference. I wasn’t stating a policy of WHO or anything like that. I was just trying to articulate what we know,” Van Kerkhove said Tuesday during an online Q&A event. “And in that, I used the phrase ‘very rare,’ and I think that that’s misunderstanding to state that asymptomatic transmission globally is very rare.”
She continued that the United Nations agency estimates about 16 percent of people are asymptomatic and able to transmit the virus, and some estimates indicate that up to 40 percent of all transmissions could be occurring through asymptomatic people.
“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.”
She also stressed that asymptomatic people are separate from patients who exhibit mild symptoms. Infected people who will go on to experience symptoms can also sometimes transmit the virus before those symptoms manifest.
Van Kerkhove’s latest remarks come after a Monday press briefing at the WHO headquarters in Geneva, where she said that, “from the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual.”
“We have a number of reports from countries who are doing very detailed contact tracing,” Van Van Kerkhove continued during the press briefing. “They’re following asymptomatic cases. They’re following contacts. And they’re not finding secondary transmission onward. It’s very rare.”
Van Kerkhove continued Monday that while additional research and data is necessary to determine how much the coronavirus can spread through people with no symptoms, asymptomatic people are not the “main driver” of new infections, and governments should focus on those who are experiencing symptoms, making sure they isolate and tracing their contacts with other people.
“If we actually followed all of the symptomatic cases, isolated those cases, followed the contacts and quarantined those contacts, we would drastically reduce” the scope of the pandemic, she remarked.
During Tuesday’s Q&A, Dr. Mike Ryan, executive director of the WHO’s emergencies program said Van Kerkhove’s previous remarks on asymptomatic transmission may have been “misinterpreted or maybe we didn’t use the most elegant words to explain that.”
“There is much to be answered on this. There is much that is unknown,” he said.
After Monday’s press briefing, the WHO was criticized by health experts who argued that the potential for asymptomatic individuals to transmit the pathogen is not negligible.
“All of the best evidence suggests that people without symptoms can and do readily spread” the coronavirus, Harvard’s Global Health Institute said in a statement, adding that the WHO “created confusion” with its original claims about asymptomatic spread.
“It’s been the Achilles heel of this outbreak. The threat of asymptomatic spread, it’s real and substantial,” Dr Ashish K Jha, the Institute’s director said.