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Most people who are infected by the SARS-CoV-2 virus, which causes Covid-19, are not asymptomatic during the course of infection, a review of studies conducted at the beginning of the pandemic suggests.
While some people who contract the new coronavirus never experience any symptoms, there is disagreement about the proportion of total infections these cases represent.
The latest study, published in the journal PLOS Medicine, suggests that true asymptomatic cases of SARS-CoV-2 comprise a minority of infections.
According to researchers from the University of Bern, Switzerland and their colleagues, the full spectrum and severity distribution of Covid-19 symptoms are not well understood.
Some people with the virus can experience serious infections that result in viral pneumonia, respiratory distress syndrome, and death, while others remain completely asymptomatic or develop mild, nonspecific symptoms.
The researchers wanted to better understand the proportion of people who become infected with SARS-CoV-2 and never develop any symptoms, as well as the proportion of people who are asymptomatic at the time of diagnosis but develop symptoms later.
They systematically reviewed the literature using a SARS-CoV-2 evidence database between March and June 2020.
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 never developed symptoms.
While the study was limited by its inability to determine the impact of false negatives, the researchers were able to estimate that 20 percent of Covid-19 infections remained asymptomatic during follow-up.
Accurate estimates of true asymptomatic and presymptomatic infections are critical to understanding the transmission of SARS-CoV-2 at the population level and for populations to adopt appropriately tailored public health strategies, the researchers said.
Greater precision of serological tests is also needed to reduce the number of false negatives, they said.
Since each person infected with SARS-CoV-2 is initially asymptomatic, it is estimated that the proportion who will develop symptoms will be around 80%, suggesting that presymptomatic transmission may contribute significantly to general SARS CoV-2 epidemics.
“The findings of this systematic review of publications at the beginning of the pandemic suggest that the majority of SARS-CoV-2 infections are not asymptomatic during the course of infection,” said Diana Buitrago-García of the University of Bern.
“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.” , Additional Buitrago-García.
