News Scan for May 27, 2022

Asymptomatic COVID-19 may not spread as easily as symptomaticSymptomatic COVID-19 cases are responsible for more viral transmission than asymptomatic infections, suggests an updated systematic review and meta-analysis of 130 studies published yesterday in PLOS Medicine.A team led by University of Bern researchers in Switzerland searched databases through Jul 6, 2021, for studies on COVID-19 patients with documented symptom status at the start and end of follow-up, as well as mathematical modeling studies.

The studies included data on 28,426 COVID-19 patients from 42 countries, 11,923 (42%) of whom were asymptomatic.Because heterogeneity among the studies was high, the team didn't estimate the average proportion of asymptomatic cases overall or in 84 screening studies of defined populations.In 46 contact-tracing or outbreak studies, the total share of asymptomatic COVID-19 cases was 19% (95% confidence interval [CI], 15% to 25%; prediction interval [PI], 2% to 70%).

Relative to symptomatic infections, the rate of viral spread from asymptomatic index patients to contacts was about two-thirds lower (risk ratio, 0.32; 95% CI, 0.16 to 0.64; PI, 0.11 to 0.95; 8 studies).

Thirteen modeling studies fit to data revealed that the proportion of all viral transmission from presymptomatic patients was higher than that of those who were asymptomatic."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 researchers wrote.But they cautioned that the study was limited by high heterogeneity and high risks of selection and information bias in studies not designed