JMIR Publications

ABSTRACT

Background:

The outbreak of coronavirus disease 2019 (COVID-19) has been declared a pandemic by the World Health Organization, while the estimates of several key epidemiological parameters of the disease by many studies were based on small sample sizes or inaccurate due to various issues.

Objective:

This study aimed to obtain more robust estimates of the incubation period, serial interval, frequency of pre-symptomatic transmission, and basic reproduction number (R0) of COVID-19.

Methods:

We systematically retrieved and screened 20909 reports of laboratory confirmed COVID-19 cases released by the health authorities of China, Japan, Singapore and Vietnam and 9942 publications retrieved from PubMed and CNKI through April 8, 2020. To be eligible, a report had to contain individual data that allowed for accurate estimation of at least one parameter. Widely used models such as lognormal distributions were fitted to the datasets and the results with best-fitting values were presented.

Results:

In total, 1605 cases were included for the final analysis. The mean and standard deviation were estimated to be 7.04 days and 4.27 days, respectively, for incubation period (n=693), and 6.49 days and 4.94 days, respectively, for serial interval (n=1024 pairs). In 40 (5.77%) cases, the incubation period was longer than 14 days. In 32 (3.13%) infector-infectee pairs, infectees’ symptom onsets occurred before those of infectors. Pre-symptomatic transmission occurred in 131 (43.67%) infector-infectee pairs (n=300 pairs). R0 was estimated to be 1.75 (95% CI: 1.69-1.82).

Conclusions:

This study provides robust estimates of several epidemiological parameters of COVID-19. The findings support current practice of 14-day quarantine of persons with potential exposure, but also suggest the need for additional measures. Pre-symptomatic transmission together with the asymptomatic transmission reported by previous studies highlight the importance of adequate testing, strict quarantine and social distancing.