Infectivity, susceptibility, and risk factors associated with SARS-CoV-2 transmission under intensive contact tracing in Hunan, China

Hu, Shixiong; Wang, Wei; Wang, Yan; Litvinova, Maria; Luo, Kaiwei; Ren, Lingshuang; Sun, Qianlai; Chen, Xinghui; Zeng, Ge; Li, Jing; Liang, Lu; Deng, Zhihong; Zheng, Wen; Li, Mei; Yang, Hao; Guo, Jinxin; Wang, Kai; Chen, Xinhua; Liu, Ziyan; Yan, Han; Shi, Huilin; Chen, Zhiyuan; Zhou, Yonghong; Sun, Kaiyuan; Vespignani, Alessandro; Viboud, Cécile; Gao, Lidong; Ajelli, Marco; Yu, Hongjie

Several mechanisms driving SARS-CoV-2 transmission remain unclear. Based on individual records of 1178 potential SARS-CoV-2 infectors and their 15,648 contacts in Hunan, China, we estimated key transmission parameters. The mean generation time was estimated to be 5.7 (median: 5.5, IQR: 4.5, 6.8) days, with infectiousness peaking 1.8 days before symptom onset, with 95% of transmission events occurring between 8.8 days before and 9.5 days after symptom onset. Most transmission events occurred during the pre-symptomatic phase (59.2%). SARS-CoV-2 susceptibility to infection increases with age, while transmissibility is not significantly different between age groups and between symptomatic and asymptomatic individuals. Contacts in households and exposure to first-generation cases are associated with higher odds of transmission. Our findings support the hypothesis that children can effectively transmit SARS-CoV-2 and highlight how pre-symptomatic and asymptomatic transmission can hinder control efforts.