A study published by the peer-reviewed journal Nature found no transmission of the coronavirus among people in close contact with asymptomatic patients.
The study in Wuhan, China, identified 300 asymptomatic coronavirus cases and followed 1,174 of their close contacts, the Epoch Times reported.
None of the contacts tested positive for COVID-19.
"Compared with symptomatic patients," the researchers said, "asymptomatic infected persons generally have low quantity of viral loads and a short duration of viral shedding, which decrease the transmission risk of SARS-CoV-2."
Being asymptomatic is not the same as being presymptomatic. An asymptomatic carrier is infected with the virus but never displays symptoms. Presymptomatic describes a phase in which a person has yet to show symptoms and can transmit the virus.
"This study confirms what physicians have known and non-scientists have suspected for millennia: namely, that asymptomatic transmission has never been the primary cause of outbreaks," Dr. Simone Gold, the founder of America’s Frontline Doctors, told the Epoch Times in an email.
The Epoch Times noted the the responses to the 2003 SARS outbreak and the 2012 MERS outbreak focused on symptomatic cases. And the Infectious Diseases Society of America's most updated guidance recommends that only people with symptoms get tested for influenza.
Sweden has based its policy of not imposing lockdowns, masks and universal testing on its belief that asymptomatic spread "accounts for a small proportion."
The Swedish Public Health Agency advises citizens to avoid infection by not touching their face, physically distancing in public places, practicing hand hygiene, sneezing or coughing into the arm fold and staying home when feeling sick.
In the United States, the Centers for Disease Control and Prevention says cloth masks should be worn in the community because there's a 50% transmission rate of asymptomatic and presymptomatic people, without differentiating between the two.
"Masks are primarily intended to reduce the emission of virus-laden droplets ("source control"), which is especially relevant for asymptomatic or presymptomatic infected wearers ... who are estimated to account for more than 50 [percent] of transmissions."
WHO official walked back 'very rare' claim
The World Health Organization's top infectious disease epidemiologist caused a stir on June 8 when she said coronavirus transmission by asymptomatic individuals is "very rare."
A day later, Dr. Maria Van Kerkhove walked back her statement, saying there had been "misunderstandings." She said on a Facebook Live video that asymptomatic people can in fact spread the virus, although it's unknown to what degree they can.
"We do know that some people who are asymptomatic or some people who don't have symptoms can transmit the virus on," she said. "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."
In her original statement June 8, at a news briefing at the United Nations agency's Geneva headquarters, 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."
"It's very rare," she said.
Van Kerkhove said that conclusion has important implications for how to limit the spread of the coronavirus.
"What we really want to be focused on is following the symptomatic cases," she said.
"If we actually followed all of the symptomatic cases, isolated those cases, followed the contacts and quarantined those contacts, we would drastically reduce" the outbreak.
That was the strategy undertaken by South Korea, which has been credited with successfully containing the virus while keeping businesses open.
Critics said Kerkhove failed in her original remarks to distinguish between asymptomatic and presymptomatic individuals, who do transmit the disease. A small study published by Nature in April that found COVID-19 patients may be most contagious two to three days before symptoms appear.