WASHINGTON (AP) — A new study from the Journal of the American Medical Association suggests that asymptomatic infections account for more than half of all COVID-19 cases.
That means identifying and isolating people with COVID symptoms isn’t enough to control the spread of the disease, according to the study.
Medical experts have shifted their views on asymptomatic spread over the course of the past year. Asymptomatic transmission means an individual can spread the disease without realizing it, and the phenomenon has led to many of the severe lockdowns this year, according to CNBC. The World Health Organization says people can even spread while they’re pre-symptomatic, or just before they begin to display symptoms, the outlet reported.
Last January, America’s top infectious disease expert, Director of National Institute of Allergy and Infectious Diseases Anthony Fauci, said that asymptomatic transmission historically has never been the driver of outbreaks.
“The driver of outbreaks is always a symptomatic person,” Fauci said at the Jan. 28 White House press briefing. “Even if there's a rare asymptomatic person that might transmit, an epidemic is not driven by asymptomatic carriers."
In June, Maria Van Kerkhove, head of the World Health Organization’s diseases and zoonosis unit, seemed to confirm his statement by saying that asymptomatic spread was very rare.
“From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual,” she said at a news briefing, according to CNBC.
WHO officials the following day walked back Kerkhove’s comments after receiving criticism from several epidemiologists across the world, CNBC reported.
"We do know that some people who are asymptomatic or some people who don't have symptoms can transmit the virus on," Kerkhove said, according to Fox News. "What we need to better understand is how many people in the population don't have symptoms and, separately, how many of those individuals go on to transmit to others."
Kerkhove clarified that she was not describing global spread, but only two or three studies, Fox reported.
"In that I used the phrase 'very rare,' and I think that's a misunderstanding to state that asymptomatic transmission globally is very rare," she said. "What I was referring to is a subset of studies."
Other modeling suggests asymptomatic people contribute to up to 40% of the virus spread, she said, according to Fox.
Fauci also flipped his position on asymptomatic spread. Two months after Kerkhove's press briefing, he described asymptomatic cases as a “driving factor” in community spread, according to CNN.
“It isn't easily identifiable who these spreaders are,” said Fauci. “That makes it much more difficult to contain.”
Further confusing the discussion, researchers found later in August that “asymptomatic cases were least likely to infect their close contacts,” according to a study of people living in Guangzhou, China, published in the Annals of Internal Medicine.
Then, in the JAMA study published Jan. 7, researchers found that about 35% of asymptomatic spreaders are pre-symptomatic, while 24% never actually develop symptoms. This means that regularly issuing COVID tests and temperature checks often won’t catch silent carriers, according to the HuffPost.