The World Health Organization's top official said Wednesday that the agency "could always do better" following confusing comments made Monday about asymptomatic transmission of the coronavirus.
Covid-19 is a new virus and the organization is learning all the time, WHO Director-General Tedros Adhanom Ghebreyesus said during a news conference at the agency's Geneva headquarters.
"Communicating complex science in real time about a new virus is not always easy, but we believe it's part of our duty to the world and we can always do better," he said. "We welcome constructive debate and that's how science advances. WHO advice will continue to evolve as new information becomes available."
The WHO drew criticism from the scientific community and others across social media Monday after one of its top scientists said asymptomatic spread of the coronavirus was "very rare."
Dr. Maria Van Kerkhove, head of the WHO's emerging diseases and zoonosis unit, walked back those comments Tuesday, saying, it was a "misunderstanding" and "we don't actually have that answer yet."
"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," she said on a live Q&A streamed across multiple social media platforms. "And in that, I used the phrase 'very rare,' and I think that that's a misunderstanding to state that asymptomatic transmission globally is very rare. I was referring to a small subset of studies."
An asymptomatic person is someone infected with Covid-19 who never develops symptoms. It's not the same as a pre-symptomatic patient, who later goes on to develop symptoms. Studies have shown that people can spread the virus in the pre-symptomatic stage as well, generally one to a few days before symptoms start.
Earlier Wednesday, Dr. Anthony Fauci, the leading U.S. infectious disease expert, said the WHO's comment "was not correct."
The WHO "walked that back because there's no evidence to indicate that's the case," Fauci, director of the National Institute of Allergy and Infectious Diseases, said during an interview that aired on ABC's "Good Morning America."
"In fact, the evidence we have given the percentage of people, which is about 25% [to] 45%, of the totality of infected people likely are without symptoms," he said. "And we know from epidemiological studies that they can transmit to someone who is uninfected even when they are without symptoms."
Tedros said Wednesday that research on asymptomatic spread is "ongoing and we're seeing more and more research being done."
"But here is what we do know: That finding, isolating and testing people with symptoms, and tracing and quarantining their contacts is the most critical way to stop transmission," he said.