Estimation of incubation period distribution of COVID-19 using disease onset forward time: a novel cross-sectional and forward follow-up study

Qin Jing; Chong You; Qiushi Lin; Taojun Hu; Shicheng Yu; Xiao-Hua Zhou

1. The collection of forward time depends on the follow-up time, that is, if the follow-up time is not long enough, we would only be able to include those with a shorter incubation period in the Wuhan departure cohort. This may lead to an underestimation of the incubation period. The same limitation also applies to Backer et al and Linton et al. 5, 6 However, as explained earlier, we only included cases who left Wuhan before January 23 in this study, which leaves an average followup time of 25 days. Hence it is less likely we missed those patients with longer incubation periods based on the largest incubation period of 24 days reported in Guan et al. 4 Note that the 24-day incubation period was reported as an outlier in Guan et al. 4 2. We assume that the individuals included in our cohort were either infected in Wuhan or on the way to their destination from Wuhan, violation of such assumption lead to an overestimation of incubation period. The same limitation also applies to Backer et al and Linton et al. 5, 6 However, with a carefully selected cohort justified in the section of Method, the chance for an individual in the Wuhan departure cohort getting infected outside Wuhan should be relatively small.