The asymptomatic rate of COVID-19 is around 35%

Objectives:
Quantification of asymptomatic infections is fundamental for effective public health responses to the COVID-19 pandemic. Discrepancies regarding the extent of asymptomaticity have arisen from inconsistent terminology as well as conflation of index and secondary cases which biases toward lower asymptomaticity. Therefore, this review article has been conducted.

What is the asymptomatic rate of COVID-19?

Study design:
This review article included 390 studies.
Most studies were conducted in China (n = 104, 27%), followed by the United States (n = 74, 19%), Italy (n = 21, 5%) and South Korea (n = 13, 3%). These studies included a total of 104,058 laboratory-confirmed COVID-19 cases, of which 25,050 exhibited no symptoms at the time of testing and 7,220 remained asymptomatic.

Out of the 170 studies included in the calculation of asymptomaticity, 75 had low risk of bias, 10 had moderate risk of bias and 85 had serious risk of bias.

Results and conclusions:   
The investigators found that the percentage of infections that never developed clinical symptoms and thus were truly asymptomatic, was 35.1% [95% CI = 30.7 to 39.9%].

The investigators found at the time of testing, 42.8% [95% prediction interval = 5.2 to 91.1%] of cases exhibited no symptoms, a group comprising both asymptomatic and presymptomatic infections.

The investigators found asymptomaticity was significantly lower among the elderly, at 19.7% [95% CI = 12.7 to 29.4%] compared with children at 46.7% [95% CI = 32.0 to 62.0%].

The investigators found that cases with comorbidities had significantly lower asymptomaticity compared to cases with no underlying medical conditions.

The investigators concluded that the asymptomatic rate of COVID-19 is around 35% and the asymptomatic rate of COVID-19 among elderly is lower than in children. Furthermore, cases with comorbidities have lower asymptomaticity compared to cases with no underlying medical conditions. Thus, without proactive policies to detect asymptomatic infections, such as rapid contact tracing, prolonged efforts for pandemic control may be needed even in the presence of vaccination.

Original title:
Asymptomatic SARS-CoV-2 infection: A systematic review and meta-analysis by Sah P, Fitzpatrick MC, […], Galvani AP.

Link:
https://www.pnas.org/content/118/34/e2109229118.long

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