Around one in four people who had evidence of past COVID-19 infection were completely asymptomatic, while 40 percent did not have one of the three classic symptoms — fever, persistent dry cough, or loss of sense of taste or smell, according to a UK study.
The UK Biobank SARS-CoV-2 Serology study was funded by the Department of Health and Social Care. It was published in the peer-reviewed online journal, BMJ, led by the chief scientist for UK Biobank and professor of epidemiology at the University of Oxford, Naomi Allen.
SARS-CoV-2 – the virus that causes COVID-19 – can produce a range of clinical manifestations, experts say; noting, however, that some people who are infected never develop any symptoms at all.
“These patients are considered true asymptomatic cases,” says Monica Gandhi, Professor of Medicine, Division of HIV, Infectious Diseases and Global Medicine, University of California, San Francisco.
Writing in the not-for-profit online media outlet, The Conversation, Gandhi states that screening for symptoms of COVID-19 and self-quarantine are good at preventing sick people from spreading the coronavirus.
“But more and more evidence is suggesting that people without symptoms are spreading the virus too,” warning that the situation may be a big part of what is driving the pandemic.
Experts say when people do get sick from the coronavirus, it takes on average five days and as many as two weeks to develop symptoms that can range from very mild to extremely dangerous.
The time between initial infection and the first symptoms is called the pre-symptomatic phase.
What this means is that anyone who came into contact with these patients without wearing a face mask, or, at least, maintaining social distancing, may have been infected without knowing.
Says Gandhi, “As an infectious disease physician, when I hear about asymptomatic spread of SARS-CoV-2, I think of a person who doesn’t have symptoms at the moment they give the virus to someone else.
“It doesn’t matter whether they are a true asymptomatic case or just pre-symptomatic; the public health risk is the same.”
According to her, those who are infected and never develop symptoms – range from 18 percent to over 80 percent of COVID-19 patients.
How can asymptomatic people spread the coronavirus?
Gandhi says that, compared to most other viral infections, SARS-CoV-2 produces an unusually high level of viral particles in the upper respiratory tract – specifically the nose and mouth.
“When those viral particles escape into the environment, that is called viral shedding,” she explains.
Researchers have found that pre-symptomatic people shed the virus at an extremely high rate, similar to the seasonal flu. But, unlike COVID-19, people with the flu don’t normally shed virus until they have symptoms.
The location of the shedding is also important, Gandhi says. “SARS-CoV – the virus that caused the SARS epidemic in 2003 – does not shed very much from the nose and mouth.
“It replicates deep in the lungs. Since SARS-CoV-2 is present in high numbers in a person’s nose and mouth, it is that much easier for the virus to escape into the environment.
“When people cough or talk, they spray droplets of saliva and mucus into the air. Since SARS-CoV-2 sheds so heavily in the nose and mouth, these droplets are likely how people without symptoms are spreading the virus,” she adds.
Even without knowing the exact numbers, the Centers for Disease Control and Prevention believes that transmission from people without symptoms is a major contributor to the rapid spread of SARS-CoV-2 around the world.
The bottom line: Wear face mask when in public place, avoid large gathering, wash your hands regularly with soap and water, apply hand sanitisers as often as possible, and, maintain social distancing.
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