An international systematic review found that people with COVID-19 who don’t have any symptoms are less contagious than those who develop symptoms.

Asymptomatic SARS-CoV-2 infections are less likely than symptomatic infections to spread COVID-19.

In most studies, the rate of asymptomatic infection is 50% or lower, according to a review of 130 different studies.

According to research reported up to July 2021, the majority of SARS-CoV-2 infections were not chronically asymptomatic, and silent infections were less contagious than symptomatic infections. Diana Buitrago-Garcia of the University of Bern, Switzerland, and colleagues published an update of a systematic review and meta-analysis on today in the open access journal PLOS Medicine.

Much research is still being done on the level and risks of asymptomatic SARS-CoV-2 infections. Because those who develop symptoms later are wrongly labeled as asymptomatic rather than presymptomatic, studies that examine participants at only one time point may overestimate the proportion of real asymptomatic infections. However, other studies with study strategies that are more likely to include symptomatic people may underestimate asymptomatic infections.

The new report is an update of a living (as in, frequently updated) systematic review that was first published in April 2020 and now contains more current findings through July 2021. There were 130 studies included, containing data on 28,426 persons infected with SARS-CoV-2 from 42 countries, including 11,923 people who were asymptomatic. The meta-analysis did not establish a single estimate for asymptomatic infection rate due to high diversity between included studies, but it did estimate the inter-quartile range to be 14–50 percent of infections were asymptomatic. Furthermore, the secondary attack rate—a measure of the risk of SARS-CoV-2 transmission—was almost two-thirds lower in persons without symptoms than in those with symptoms (risk ratio 0.32, 95 percent CI 0.16–0.64), according to the researchers.

““If both the proportion and transmissibility of asymptomatic infection are relatively low, people with asymptomatic SARS-CoV-2 infection should account for a smaller proportion of overall transmission than presymptomatic individuals,” the authors write, adding that “when SARS-CoV-2 community transmission levels are high, physical distancing measures and mask-wearing need to be sustained to prevent transmission from close contact with people with asymptomatic and presymptomatic infection.”

“The true proportion of asymptomatic SARS-CoV-2 infection is still not known,” says coauthor Nicola Low, “and it would be misleading to rely on a single number because the 130 studies that we reviewed were so different. People with truly asymptomatic infection are, however, less infectious than those with symptomatic infection.”

Image Credit: Getty

You were reading: Symptomatic COVID Is More Infectious Than Asymptomatic – New Research Finds