BACKGROUND: Understanding the epidemiological parameters that determine the 
transmission dynamics of COVID-19 is essential for public health intervention. 
Globally, a number of studies were conducted to estimate the average serial 
interval and incubation period of COVID-19. Combining findings of existing 
studies that estimate the average serial interval and incubation period of 
COVID-19 significantly improves the quality of evidence. Hence, this study aimed 
to determine the overall average serial interval and incubation period of 
COVID-19.
METHODS: We followed the PRISMA checklist to present this study. A comprehensive 
search strategy was carried out from international electronic databases (Google 
Scholar, PubMed, Science Direct, Web of Science, CINAHL, and Cochrane Library) 
by two experienced reviewers (MAA and DBK) authors between the 1st of June and 
the 31st of July 2020. All observational studies either reporting the serial 
interval or incubation period in persons diagnosed with COVID-19 were included 
in this study. Heterogeneity across studies was assessed using the I2 and 
Higgins test. The NOS adapted for cross-sectional studies was used to evaluate 
the quality of studies. A random effect Meta-analysis was employed to determine 
the pooled estimate with 95% (CI). Microsoft Excel was used for data extraction 
and R software was used for analysis.
RESULTS: We combined a total of 23 studies to estimate the overall mean serial 
interval of COVID-19. The mean serial interval of COVID-19 ranged from 4. 2 to 
7.5 days. Our meta-analysis showed that the weighted pooled mean serial interval 
of COVID-19 was 5.2 (95%CI: 4.9-5.5) days. Additionally, to pool the mean 
incubation period of COVID-19, we included 14 articles. The mean incubation 
period of COVID-19 also ranged from 4.8 to 9 days. Accordingly, the weighted 
pooled mean incubation period of COVID-19 was 6.5 (95%CI: 5.9-7.1) days.
CONCLUSIONS: This systematic review and meta-analysis showed that the weighted 
pooled mean serial interval and incubation period of COVID-19 were 5.2, and 
6.5 days, respectively. In this study, the average serial interval of COVID-19 
is shorter than the average incubation period, which suggests that substantial 
numbers of COVID-19 cases will be attributed to presymptomatic transmission.