Reassessing Early COVID-19 Strategies in East Asia: Insights From Japan and Korea.

East Asian countries had remarkably low coronavirus disease 2019 (COVID-19) mortality in 2020, a pattern widely cited as evidence of effective public health interventions. However, Japan and Korea-often classified as having followed similar early intervention strategies-adopted substantially different approaches. These differences are largely obscured by commonly used stringency indices and policy score analyses. While neither country implemented a lockdown, Korea pursued an aggressive, government-mandated strategy based on extensive testing, isolation, quarantine, and compulsory data collection. In contrast, Japan relied on a voluntary model with limited mass testing, a policy that drew strong criticism during the early phase of the pandemic. Because asymptomatic COVID-19 infection was highly prevalent, these divergent testing policies were particularly important in shaping patterns of community transmission. Using excess mortality as a comprehensive outcome metric, Japan's outcomes were as favorable as Korea's through the pre-Omicron period, despite Japan's limited testing. In 2020, excess mortality was negligible in both countries (-1.7% in Japan vs. +0.3 to +2.1% in Korea). In 2021, excess mortality increased modestly (+2.2% vs. +4.0 to +5.6%). However, in 2022, despite approximately 80% vaccination coverage in both countries, excess mortality reached +7.6% in Japan and about +20% in Korea-three times the Japanese level despite Korea's much higher booster rate. These patterns of excess mortality in 2 countries with contrasting testing strategies challenge the view that East Asia's early success stemmed primarily from stringent virus suppression measures. They highlight the need to consider alternative explanations, including the possibility that pre-existing immunity differed substantially across geographical regions.