Transmission interval estimates suggest pre-symptomatic spread of COVID-19

Lauren Tindale; Michelle Coombe; Jessica E Stockdale; Emma Garlock; Wing Yin Venus Lau; Manu Saraswat; Yen-Hsiang Brian Lee; Louxin Zhang; Dongxuan Chen; Jacco Wallinga; Caroline Colijn

There are several limitations to this work. First, the times of exposure and the presumed infectors are uncertain, and the incubation period is variable. We have not incorporated uncertainty in the dates of symptom onset. We have used the mixture model approach for serial intervals to avoid assuming that the presumed infector is always the true infector, but the mixture does not capture all possible transmission configurations. Our R0 estimates are very simple and could be refined with more sophisticated modelling in combination with case count data. We have not adjusted for truncation (eg shorter serial intervals are likely to be observed first). However, the serial interval estimates are consistent between the two datasets, are robust to the parameter choices, and are consistently shorter than the estimated incubation times.