Temporal characteristics of case profile and case isolation shaped the distributions of serial interval of COVID-19 in Hong Kong

Abstract

The serial interval distribution is used to approximate the generation time distribution, an essential parameter to predict the effective reproductive number “Rt”, a measure of transmissibility. However, serial interval distributions may change as an epidemic progresses rather than remaining constant. We examined detailed contact tracing data on laboratory-confirmed cases of COVID-19 in Hong Kong during all four waves from January 2020 to May 2021. We constructed the transmission pair data from the epidemiological link information between infector and infectee. We estimated effective serial intervals and assess the association with age and severity profile of cases and case isolation at a temporal scale. We show that serial intervals in Hong Kong varied over time with variations in patterns across the waves. The serial intervals were found to be shortened and lengthened and closely associated with the impact of temporal variation in COVID-19 case profiles and public health and social measures that were implemented in response to surges in community transmission.