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Asymptomatic cases of coronavirus may account for about 20 percent of infections, a new study suggests.
Some people who contract COVID-19 never experience any symptoms and there remains disagreement about what proportion of all infections these cases represent.
The full spectrum of symptom severity is not well understood. Some infected people may experience serious infections leading to viral pneumonia, respiratory distress syndrome, and death, while others remain completely asymptomatic or develop mild, nonspecific symptoms.
The researchers analyzed 79 studies that reported empirical data on 6,616 people, 1,287 of whom were defined as asymptomatic, to determine the proportion of infected people who did not develop symptoms.
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Although the study could not measure the impact of false negatives, the researchers estimated that 20 percent of infections remained asymptomatic during follow-up.
The researchers argue that accurate estimates of true asymptomatic and presymptomatic infections are critical to understanding population-level transmission of the virus.
“The findings of this systematic review of publications at the beginning of the pandemic suggest that the majority of SARS-CoV-2 [the virus that causes COVID-19] infections are not asymptomatic during the course of infection, ”the authors wrote.
“The contribution of presymptomatic and asymptomatic infections to the general transmission of SARS-CoV-2 means that combined prevention measures will continue to be needed, with improved respiratory and hand hygiene, testing and tracking, and isolation and social distancing strategies.” .
More accurate tests are needed to reduce the number of false negatives, the study suggests.
As each person infected with the virus is initially asymptomatic, the proportion who will develop symptoms is estimated to be around 80%, suggesting that presymptomatic transmission may contribute significantly to general SARS-CoV-2 epidemics.
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“This extensive description of multiple studies concludes that the majority of people who are infected with the coronavirus that causes COVID-19 eventually develop symptoms,” said Dr. Simon Clarke, associate professor of cell microbiology at the University of Reading.
“There has been a lot of talk about the number of people with the virus, but without symptoms. While this is very interesting, it remains true that on any given day, most people with the virus will not show any symptoms and these findings should in no way detract from current infection control advice. “
