Time-varying transmission heterogeneity of SARS and COVID-19 in Hong Kong

Abstract

<title>Abstract</title> Transmission heterogeneity is a notable feature of the severe acute respiratory syndrome (SARS) and coronavirus disease 2019 (COVID-19) epidemics, though previous efforts to estimate how heterogeneity changes over time are limited. Using contact tracing data, we compared the epidemiology of SARS and COVID-19 infection in Hong Kong in 2003 and 2020-21 and estimated time-varying transmission heterogeneity (<italic>k</italic>_t) by fitting negative binomial models to offspring distributions generated across variable observation windows. <italic>k</italic>_t fluctuated over time for both COVID-19 and SARS on a continuous scale though SARS exhibited significantly greater (p &lt; 0.001) heterogeneity compared to COVID-19 overall and in-time. For COVID-19, <italic>k</italic>_t declined over time and was significantly associated with increasingly stringent non-pharmaceutical interventions though similar evidence for SARS was inconclusive. Underdetection of sporadic COVID-19 cases led to a moderate overestimation of <italic>k</italic>_t, indicating COVID-19 heterogeneity of could be greater than observed. Time-varying or real-time estimates of transmission heterogeneity could become a critical indicator for epidemic intelligence in the future.