BACKGROUND: The aim of our study was to determine through a systematic review 
and meta-analysis the incubation period of COVID-19. It was conducted based on 
the preferred reporting items for systematic reviews and meta-analyses (PRISMA). 
Criteria for eligibility were all published population-based primary literature 
in PubMed interface and the Science Direct, dealing with incubation period of 
COVID-19, written in English, since December 2019 to December 2020. We estimated 
the mean of the incubation period using meta-analysis, taking into account 
between-study heterogeneity, and the analysis with moderator variables.
RESULTS: This review included 42 studies done predominantly in China. The mean 
and median incubation period were of maximum 8 days and 12 days respectively. In 
various parametric models, the 95th percentiles were in the range 10.3-16 days. 
The highest 99th percentile would be as long as 20.4 days. Out of the 10 
included studies in the meta-analysis, 8 were conducted in China, 1 in 
Singapore, and 1 in Argentina. The pooled mean incubation period was 6.2 (95% CI 
5.4, 7.0) days. The heterogeneity (I2 77.1%; p < 0.001) was decreased when we 
included the study quality and the method of calculation used as moderator 
variables (I2 0%). The mean incubation period ranged from 5.2 (95% CI 4.4 to 
5.9) to 6.65 days (95% CI 6.0 to 7.2).
CONCLUSIONS: This work provides additional evidence of incubation period for 
COVID-19 and showed that it is prudent not to dismiss the possibility of 
incubation periods up to 14 days at this stage of the epidemic.