While it has been claimed that up to 50% of coronavirus patients will remain asymptomatic for the duration of their infection, a new meta-analysis of several studies focusing on the experience of COVID-19 patients suggests that as many as four in five will go on to develop symptoms. The analysis, published in PLOS Medicine and conducted by researchers with the University of Bern in Switzerland, suggests that some patients described as asymptomatic at the time of the study period may later go on to develop symptoms but are unaccounted for in the data.
“The proportion of people who will remain asymptomatic throughout the course of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the cause of coronavirus disease 2019 (COVID-19), is not known,” the authors wrote. “Studies that assess people at just one-time point will overestimate the proportion of true asymptomatic infection because those who go on to develop COVID-19 symptoms will be wrongly classified as asymptomatic rather than presymptomatic.”
The authors said that by taking a closer look at this data, which included 79 studies, there could be a better understanding of the amount and infectiousness of asymptomatic SARS-CoV-2 infection, which in turn could lead to better prevention of transmission. However, they noted that not each data set was a true reflection of the population.
“If the predominate route of transmission is from people who have symptoms, then strategies should focus on testing, followed by isolation of infected individuals and quarantine of their contacts,” the study authors wrote. “If however, most transmission is from people without symptoms, social distancing measures that reduce contact with people who might be infectious should be prioritized, enhanced by active case-finding through testing of asymptomatic people.”
Through their analysis, the study authors said the data does not “support the claim that a large majority of SARS-CoV-2 infections are asymptomatic,” and instead they estimate that the proportion of COVID-19 infections that are asymptomatic throughout the infection period is around 20%.
The implications of their review, the authors argue, suggest that the “contribution of presymptomatic and asymptomatic infections to overall SARS-CoV-2 transmission means that combination prevention measures, with enhanced hand hygiene, masks, testing tracing and isolation strategies and social distancing, will continue to be needed.”