Transmission Onset Distribution of COVID-19 in South Korea

Abstract

Background: The distribution of the transmission onset of COVID-19 relative to the symptom onset is a key parameter for infection control. It is often not easy to study the transmission onset time, as is difficult to know who infected whom exactly when. Methods: We inferred transmission onset time from 72 infector-infectee pairs in South Korea, either with known or inferred contact dates by means of incubation period. Combining this data with known information of infector’s symptom onset, we could generate the transmission onset distribution of COVID-19, using Bayesian methods. Findings: We estimated the median transmission onset to be 1·31 days (standard deviation, 2·64 days) after symptom onset with peak at 0·72 days before symptom onset. The pre-symptomatic transmission proportion was 37% (95% credible interval [CI], 16–52%). The median incubation period was estimated to be 2·87 days (95% CI, 2·33–3·50 days) and the median serial interval to be 3·56 days (95% CI, 2·72–4·44 days). Interpretation: Considering the transmission onset distribution peaked with the symptom onset and the pre-symptomatic transmission proportion is substantial, the usual preventive measure might be too late to prevent SARS-CoV-2 transmission. Funding Statement: None. Declaration of Interests: The authors declare that there are no competing interests. Ethics Approval Statement: All the data used in this study were publicly available and were approved from institutional review board assessment of National Cancer Center (NCC2020-0119).