Low dispersion in the infectiousness of COVID-19 cases implies difficulty in control

He, Daihai; Zhao, Shi; Xu, Xiaoke; Lin, Qiangying; Zhuang, Zian; Cao, Peihua; Wang, Maggie H.; Lou, Yijun; Xiao, Li; Wu, Ye; Yang, Lin

The individual infectiousness of coronavirus disease 2019 (COVID-19), quantified by the number of secondary cases of a typical index case, is conventionally modelled by a negative-binomial (NB) distribution. Based on patient data of 9120 confirmed cases in China, we calculated the variation of the individual infectiousness, i.e., the dispersion parameter k of the NB distribution, at 0.70 (95% confidence interval: 0.59, 0.98). This suggests that the dispersion in the individual infectiousness is probably low, thus COVID-19 infection is relatively easy to sustain in the population and more challenging to control. Instead of focusing on the much fewer super spreading events, we also need to focus on almost every case to effectively reduce transmission.