The COVID-19 Resource Centre, established by Elsevier in January 2020, provides free information in English and Mandarin on the novel coronavirus. Elsevier grants permission to make all COVID-19-related research available in PubMed Central and other public repositories, with unrestricted reuse and analysis rights. The article discusses the estimation of the asymptomatic ratio of COVID-19 infections, which is crucial for understanding transmission and disease spectrum. The study uses data from Japanese nationals evacuated from Wuhan, China, to estimate the asymptomatic ratio. Among 565 evacuees, 63 (11.2%) were symptomatic upon arrival, and 4 out of 15 asymptomatic individuals tested positive for COVID-19. Using Bayes' theorem, the asymptomatic ratio was estimated to be 30.8% (95% CI 7.7–53.8%). This suggests that less than half of infected individuals may be asymptomatic, a lower ratio than for influenza. The study highlights the need for further research to guide epidemic control efforts, acknowledging limitations such as the small sample size and the exclusion of age-dependent factors.The COVID-19 Resource Centre, established by Elsevier in January 2020, provides free information in English and Mandarin on the novel coronavirus. Elsevier grants permission to make all COVID-19-related research available in PubMed Central and other public repositories, with unrestricted reuse and analysis rights. The article discusses the estimation of the asymptomatic ratio of COVID-19 infections, which is crucial for understanding transmission and disease spectrum. The study uses data from Japanese nationals evacuated from Wuhan, China, to estimate the asymptomatic ratio. Among 565 evacuees, 63 (11.2%) were symptomatic upon arrival, and 4 out of 15 asymptomatic individuals tested positive for COVID-19. Using Bayes' theorem, the asymptomatic ratio was estimated to be 30.8% (95% CI 7.7–53.8%). This suggests that less than half of infected individuals may be asymptomatic, a lower ratio than for influenza. The study highlights the need for further research to guide epidemic control efforts, acknowledging limitations such as the small sample size and the exclusion of age-dependent factors.