Transmission roles of symptomatic and asymptomatic COVID-19 cases: a modeling study

Objective Age-dependent asymptomatic and symptomatic transmission dynamics of COVID-19 have not been well quantified due to limited data. Methods Through a population-based surveillance network, we collected data on 1342 confirmed cases with a 90-days follow-up for all asymptomatic cases. Results The difference in transmissibility of a symptomatic and asymptomatic case depended on age and was most distinct for the middle-age groups. The asymptomatic cases had a 66.72% lower transmissibility rate than symptomatic cases, and 74.10% (95%CI: 65.85% - 80.72%) of all asymptomatic cases were missed in detection. The average proportion of asymptomatic cases was 28.22% (95%CI: 22.97% - 34.56%). Simulation showed that the burden of asymptomatic transmission increased as the epidemic continued and could potentially dominate the spreading. Conclusion Asymptomatic COVID-19 cases play a significant role in transmission. Vaccine Strategies prioritizing the population between 30-60 years old are likely to have the most population-level benefits.