Progress on the incubation period of COVID-19

Abstract

<p indent="0mm">Coronavirus disease 2019 (COVID-19) is an emerging infectious disease caused by SARS-CoV-2. Effective treatments are still lacking. The incubation period of COVID-19 is the period between the infection of an individual by a pathogen (SARS-CoV-2) and the manifestation of the illness or disease. The incubation period is one of the important epidemiological parameters of infectious diseases. The study of the incubation period of COVID-19 is of great significance for better understanding the natural history of the disease, tracing the source of infection, determining the detention, quarantine and isolation of contacts, determining the time of immunization, and making prevention and control measures. This study mainly reviews the progress of the incubation period of COVID-19. In previous studies, a direct calculation or parameter estimation method is usually used to estimate the incubation period, and the commonly used distributions are lognormal distribution, Weibull distribution, Gamma distribution, etc. Due to the differences in the study population, data sources and estimation methods, there are differences in the estimation results of the incubation period of COVID-19 in various studies. The estimated median incubation period for COVID-19 was about <sc>5.9 d</sc> (95%CI: 2.98−10.51) and the average incubation period was about <sc>5.7 d</sc> (95%CI: 4.3−8.9). The median incubation period for COVID-19 was estimated to be about <sc>5.2 d</sc> (95%CI: 3.0−11.9) in studies using the direct calculation method, and about <sc>5.25 d</sc> (95%CI: 3.57−8.19) in studies using the parameter estimation method. To calculate the incubation period of COVID-19, it is important to accurately collect the date of exposure and the date of symptoms onset. Due to the diversity of COVID-19 transmission routes and the possibility of multiple exposures to the same source of infection or to different sources of infection, it is often difficult to determine the exact exposure time for some patients, which brings the difficulty to the accurate estimation of the incubation period. The choice of methods depends on the epidemiological data of the study population and application scenarios. For example, in the early stage of an outbreak, when the incubation period data of small samples of infected persons are quickly obtained through field epidemiological investigation, it is advisable to adopt the direct calculation method for rapid estimation and timely guidance for prevention and control measures. As the epidemic progresses, when more epidemiological survey data are available, the parameter estimation method is a better choice. The optimal method can be selected for estimation. Either direct calculation or parameter estimation method, the accuracy of the data is crucial. Therefore, the recall bias should be minimized to obtain relatively accurate data at each key time point. At the same time, a more accurate estimate of the incubation period can be obtained by taking the infector-infected pairs with a clear transmission chain as the study population.