Up to 41% of people infected with Covid-19 may be asymptomatic and a better understanding of how many people transmit the disease is needed, an expert from the World Health Organization (WHO) said.
In a briefing on Tuesday, Maria Van Kerkhove, WHO technical leadership Covid-19, said some modeling groups estimate that about 40% of coronavirus transmission may be due to asymptomatic cases.
She said research estimates suggest that the percentage of people with Covid-19 who are asymptomatic may be anywhere from 6% to 41%.
Dr. Kerkhove tried to clarify the comments she made Monday suggesting that transmission of coronavirus by people without symptoms was “very rare.”
She told the previous WHO briefing, “We have a number of reports from countries doing very detailed contact tracking.
“They follow asymptomatic cases, they follow contacts and they don’t find a secondary transmission. It’s very rare.”
But on Tuesday, she explained that she was talking about “one or two or three studies.”
She added, “I responded to a question during the press conference. I was not talking about a WHO policy or anything like that. I was just trying to articulate what we know.
“And in that I used the phrase” very rare, “and I think that’s a misunderstanding to say that asymptomatic transmission is very rare worldwide. What I was referring to was a subset of studies.”
She said the WHO also relied on unpublished data from its member states.
Liam Smeeth, professor of clinical epidemiology at the London School of Hygiene and Tropical Medicine, responded to Dr.’s “very rare” comment. Kerkhove: “I was quite surprised by the WHO statement and I have not seen the data on which the statement is based.
“It goes against my impressions of science so far that suggest that asymptomatic people – who never get symptoms – and pre-symptomatic people are a major source of infection for others.
“This is the main basis for steps such as self-insulation and locking.”
Dr. Kerkhove also said on Tuesday, “Most of the transmission we know is that people with symptoms transmit the virus to other people through infectious drops, but there is a subgroup of people who don’t develop symptoms and to really understand how many people have no symptoms we don’t have that answer yet.
“There are some estimates that suggest anywhere between 6% and 41% of the population may be infected but have no symptoms, with a point estimate of about 16%.
“We do know that some people who are asymptomatic or some people who have no symptoms can transmit the virus.
“And so what we need to understand better is how many of the people in the population have no symptoms and how many of those individuals pass on to others individually.”
Dr. Kerkhove said some modeling groups have attempted to estimate “what is the proportion of asymptomatic people who can transmit”.
She continued, “And these are estimates and there is a wide range of different models depending on how the models are done, where they are done, from which country.
But some estimates of about 40% of the transmission may be due to asymptomatic. But they come from models. ‘
Keith Neal, professor emeritus of epidemiology of infectious diseases at the University of Nottingham, said: “How much role asymptomatic transmission plays in the total number of new infections remains unclear, but symptomatic people are responsible for most new infections of Covid -19.
“This reinforces the importance of any person who has any of the symptoms of Covid-19 to arrange and isolate a test for themselves as soon as possible until they get their test result.”