Estimating the Generation Time and Relative Infectiousness from Contact Tracing Data

• Activity Number: 373 - Analysis of Duration Data, with Applications to the COVID-19 Pandemic
• Type: Topic-Contributed
• Date/Time: Thursday, August 12, 2021 : 12:00 PM to 1:50 PM
• Sponsor: IMS
• Author(s): Hiroshi Nishiura*
• Companies: Kyoto University School of Public Health
• Keywords: Inapparent infection; Subclinical infection; Transmissibility; Mathematical model; Contact tracing

Abstract

Japan conducted the retrospective contact tracing as part of countermeasures against coronavirus disease 2019 (COVID-19), offering critical insights into the actual transmission networks. Movement of all close contact was restricted for 14 days and they underwent laboratory testing with polymerase chain reaction. Here we estimated the generation time from contact tracing data. Using the most plausible event date of transmission and investigating the secondary-tertiary case pairs, we show that the generation time can be directly inferred from such epidemiological investigation data. Moreover, we observe that the incubation period of primary case is positively correlated with the generation time. Using the very first cluster datasets in Tokyo and Kanagawa (n=36) and Kyoto (n=50), the reproduction number for symptomatic cases was estimated to be 1.2 (95% confidence interval (CI): 0.5-2.9) and the relative infectiousness of asymptomatically infected cases was estimated to be 0.27 (95% CI: 0.03-0.81) of symptomatic cases. The relative transmissibility of asymptomatic cases is limited. Observing clusters starting with symptomatic transmission might be sufficient for the control.