Background: By March, 2021, the COVID-19 outbreak had reached its highest peak at the end of December, 2020. Nevertheless, no remarkable excess mortality attributable to COVID-19 has been observed. Object: We sought to quantify excess mortality in April using the National Institute of Infectious Diseases (NIID) model. Method: We applied the NIID model to deaths of all causes from 1987 through February, 2021 for all of Japan and through October for Tokyo. Results: Results obtained for Japan show very few excess mortality cases in August and October, 2020, estimated respectively as 12 and 104. However, in Tokyo, 595 cases of excess mortality were detected during August and October: they were, respectively, 3.1% and 1.7% of baseline numbers. Discussion and Conclusion: We detected considerable excess mortality in Tokyo but not throughout Japan. Continued careful monitoring of excess mortality of COVID-19 is expected to be important.

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