Epidemiological parameters of coronavirus disease 2019: a pooled analysis of publicly reported individual data of 1155 cases from seven countries

Shujuan Ma; Jiayue Zhang; Minyan Zeng; Qingping Yun; Wei Guo; Yixiang Zheng; Shi Zhao; Maggie H Wang; Zuyao Yang

Our estimates of incubation period and serial interval are longer than most of the previous estimates. [2] [3] [4] [5] [6] [7] There are several possible reasons for the difference. First, the sample size is generally small in previous studies, 2, 4, 6, 7, [9] [10] [11] [12] but much larger in the present one. Second, most cases in previous studies had a long or even unclear interval of exposure, making it difficult to determine the exact exposure date 3, 5, 13 and giving rise to error. By contrast, this study followed strict inclusion criteria regarding exposure period and method to determine exposure date to ensure the potential error in the estimates be small (< 0.3 day, according to the sensitivity analysis). Third, the approaches to determination of transmission order within clusters are different. For the cases involving cluster infection, which represent the majority of all cases, a common practice of previous studies was to take the case with earliest date of symptom onset as infector and others as infectee. 9 However, we deemed it inappropriate in view of the varying incubation periods of individuals and potential pre-symptomatic or asymptomatic transmission.