Epidemiological characteristics and incubation period of SARS-CoV-2 during the 2020-2021 winter pandemic wave in North China: An observational study.

As the emergence of new variants of SARS-CoV-2 persists across the world, it is of importance to understand the distributional behavior of the incubation period of the variants for both medical research and public health policy-making. We collected the published individual-level data of 941 patients of the 2020-2021 winter pandemic wave in Hebei province, North China. We computed some epidemiological characteristics of the wave and estimated the distribution of the incubation period. We further assessed the covariate effects of sex, age, and living with a case with respect to the incubation period by a model. The infection-fatality rate was only 0.1%. The estimated median incubation period was at least 22 days, significantly extended from the estimates (ranging from 4 to 8.5 days) of the previous wave in mainland China and those ever reported elsewhere around the world. The proportion of asymptomatic patients was 90.6%. No significant covariate effect was found. The distribution of incubation period of the new variants showed a clear extension from their early generations.