Temporal dynamics in viral shedding and transmissibility of COVID-19

Xi He; Eric HY Lau; Peng Wu; Xilong Deng; Jian Wang; Xinxin Hao; Yiu Chung Lau; Jessica Y Wong; Yujuan Guan; Xinghua Tan; Xiaoneng Mo; Yanqing Chen; Baolin Liao; Weilie Chen; Fengyu Hu; Qing Zhang; Mingqiu Zhong; Yanrong Wu; Lingzhai Zhao; Fuchun Zhang; Benjamin J Cowling; Fang Li; Gabriel M Leung

Separately, based on 77 transmission pairs obtained from publicly available sources within and outside mainland China, the serial interval was estimated to have a mean of 5.8 days (95% confidence interval [CI] = 4.8 to 6.8) and median of 5.2 days (95% CI = 4.1 to 6.4) based on a fitted gamma distribution ( Figure 1b) . Assuming an incubation period with a mean of 5.2 days from a separate study of early COVID-19 cases, 2 we inferred that infectiousness started from 2.5 days before symptom onset and reached its peak at 0.6 days before symptom onset (Figure 1b) . The proportion of transmission before symptom onset (area under the curve) was 44%. Infectiousness was estimated to decline relatively quickly within 7 days of illness onset. Viral load data was not used in the estimation but showed similar monotonic decreasing pattern after symptom onset.