Abstract
A novel coronavirus disease, designated as COVID-19, has become a pandemic worldwide. This study aims to estimate the incubation period and serial interval of COVID-19. We collected contact tracing data in a municipality in Hubei province during a full outbreak period. The date of infection and infector-infectee pairs were inferred from the history of travel in Wuhan or exposed to confirmed cases. The incubation periods and serial intervals were estimated using parametric accelerated failure time models, accounting for interval censoring of the exposures. Our estimated median incubation period of COVID-19 is 5.4 days (bootstrapped 95% confidence interval (CI) 4.8-6.0), and the 2.5th and 97.5th percentiles are 1 and 15 days, respectively; while the estimated serial interval of COVID-19 falls within the range of -4 to 13 days with 95% confidence and has a median of 4.6 days (95% CI 3.7-5.5). Ninety-five per cent of symptomatic cases showed symptoms by 13.7 days (95% CI 12.5-14.9). The incubation periods and serial intervals were not significantly different between male and female, and among age groups. Our results suggest a considerable proportion of secondary transmission occurred prior to symptom onset. And the current practice of 14-day quarantine period in many regions is reasonable.
Highlights
A novel coronavirus disease, designated as COVID-19, has become a pandemic worldwide
Incubation period is the basis of the quarantine period for suspicious cases [4, 5]; while serial interval can help to estimate generation interval and reproduction number of an infectious disease [6, 7]
Our study shows that the incubation period of COVID-19 follows a Weibull distribution, and the serial interval follows an approximately normal distribution
Summary
A novel coronavirus disease, designated as COVID-19, has become a pandemic worldwide. As of 29 March 2020, there were 634 835 confirmed COVID-19 cases and 29 957 deaths reported worldwide [1]. Incubation period and serial interval are two key indicators that aid to depict the transmission dynamics of infectious infections [3]. Incubation period is the basis of the quarantine period for suspicious cases [4, 5]; while serial interval can help to estimate generation interval and reproduction number of an infectious disease [6, 7]. The reported median incubation periods of COVID-19 varied from 4 [8] to 8 days [9]. The above-mentioned studies have been limited by the small sample sizes and/or the fact that using publicly reported data. As a result, sampling bias and selection bias may have been introduced into the estimates [12]
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