Median 5-Day Incubation Period for COVID-19

The median incubation period for coronavirus disease 2019 (COVID-19) is approximately 5 days, according to study results published in medRxiv.

The first case of COVID-19 was identified in China in December 2019; however, there are limited data on the incubation period for COVID-19, which has estimated the range to be between 2 days and 14 days. The incubation period for COVID-19 has important implications for public health activities, including active monitoring, surveillance, modeling, and disease control. The objective of this study was to gain a better understanding of the COVID-19 incubation period and estimate its length as well as to examine its implications on public health.

Therefore, researchers performed a pooled analysis of data on 181 patients outside Hubei, China, with confirmed COVID-19. English and Chinese news reports and press releases from 50 provinces, regions, and countries were utilized, and data including cases reported between January 4 and February 24, 2020, were used in the analysis. Researchers recorded the dates and times of possible disease exposure for each patient (either via travel history or under the assumption of the maximum possible interval of exposure to an infected person) as well as symptom onset, fever onset, and case detection. Incubation time was estimated using a parametric accelerated failure time model under the assumption that incubation time followed log-normal distribution similar to that observed in other acute respiratory viral infections.

Researchers revealed that the median incubation period for COVID-19 was 5.1 days (95% CI, 4.5-5.8 days). Fewer than 2.5% of patients infected with COVID-19 were estimated to show symptoms within 2.2 days (95% CI, 1.8-2.9 days) of exposure, and 97.5% of patients infected with COVID-19 were estimated to develop symptoms within 11.5 days (95% CI, 8.2-15.6 days). Using these estimates, researchers predicted that after 14 days of active monitoring or quarantine, 101 in every 10,000 patients incubated for COVID-19 would develop symptoms.

Limitations to this study included possible inaccuracy in the intervals of disease exposure and symptom onset, as well as the overrepresentation of patients with severe symptoms, which may have affected incubation period estimates.

The study researchers concluded that the median incubation period for COVID-19 is 5 days (similar to that for severe acute respiratory syndrome) and that results support current proposals for the length of quarantine for patients potentially exposed to COVID-19.

Reference

Lauer SA, Grantz KH, Bi Q, et al. The incubation period of 2019-nCoV from publicly reported confirmed cases: estimation and application [published online March 9, 2020]. Ann Intern Med. doi:10.7326/M20-0504