OBJECTIVE: To estimate the incubation period of Vietnamese confirmed COVID-19 
cases.
METHODS: Only confirmed COVID-19 cases who are Vietnamese and locally infected 
with available data on date of symptom onset and clearly defined window of 
possible SARS-CoV-2 exposure were included. We used three parametric forms with 
Hamiltonian Monte Carlo method for Bayesian Inference to estimate incubation 
period for Vietnamese COVID-19 cases. Leave-one-out Information Criterion was 
used to assess the performance of three models.
RESULTS: A total of 19 cases identified from 23 Jan 2020 to 13 April 2020 was 
included in our analysis. Average incubation periods estimated using different 
distribution model ranged from 6.0 days to 6.4 days with the Weibull 
distribution demonstrated the best fit to the data. The estimated mean of 
incubation period using Weibull distribution model was 6.4 days (95% credible 
interval (CrI): 4.89-8.5), standard deviation (SD) was 3.05 (95%CrI 3.05-5.30), 
median was 5.6, ranges from 1.35 to 13.04 days (2.5th to 97.5th percentiles). 
Extreme estimation of incubation periods is within 14 days from possible 
infection.
CONCLUSION: This analysis provides evidence for an average incubation period for 
COVID-19 of approximately 6.4 days. Our findings support existing guidelines for 
14 days of quarantine of persons potentially exposed to SARS-CoV-2. Although for 
extreme cases, the quarantine period should be extended up to three weeks.