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

Abstract

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.

INTRODUCTION

In 2020, the first year of the coronavirus disease 2019 (COVID-19) pandemic, East Asian countries recorded much lower COVID-19 mortality rates than Western countries, including those in Europe and the United States [1]. Despite their geographic proximity to Wuhan, China—the initial epicenter of the outbreak—countries in this region maintained remarkably low infection and mortality rates [1]. These favorable outcomes have generally been attributed to early public health interventions aimed at suppressing transmission, together with strong individual behavioral responses, including widespread mask use and high compliance with public health guidelines [2].

Overall stringency indices and specific policy scores—such as those from the Oxford COVID-19 Government Response Tracker—were widely used to compare non-pharmaceutical interventions across countries during the COVID-19 pandemic [3]. Although these metrics provide continuously updated information for policy assessment, they cannot fully capture nuanced but critical differences in national responses. Consequently, important variations in national strategies—often essential for evaluating the real-world effectiveness of public health measures—may be overlooked.

For instance, East Asian countries are often grouped together as if they had followed the same early pandemic strategy [4]. However, their initial responses—particularly those of Japan and Korea—differed far more than is commonly assumed. Japan implemented a less restrictive, voluntary approach, a decision that initially drew strong criticism [5]. At the time, rapid lockdowns or mass testing were widely regarded as essential for controlling viral spread [6,7]. Although neither country imposed lockdowns, Korea adopted extensive mass testing, whereas Japan used neither lockdowns nor widespread testing [5].

These neighboring countries share key demographic and systemic characteristics relevant to pandemic dynamics, including high population density, universal healthcare systems, comparable socioeconomic conditions, and rapidly aging populations. Given these shared features, a careful narrative comparison of their early policies and pandemic outcomes—grounded in published evidence—may provide insights that standard analyses overlook. Although narrative comparisons are often dismissed as crude or inferior to quantitative approaches, purely numerical analyses may miss hidden factors that ultimately shape real-world outcomes. This article may therefore help reassess prevailing assumptions about the effectiveness of public health measures focused primarily on suppressing viral transmission.

DIFFERENCES IN EARLY TESTING POLICIES BETWEEN JAPAN AND KOREA

The key difference between Japan and Korea lay in their approaches to case detection. COVID-19 is characterized by a high prevalence of asymptomatic infection [8], and individuals who are asymptomatic or pre-symptomatic can transmit the virus [9]. Therefore, even if all other public health measures had been identical, differences in case detection policies alone could have substantially shaped the extent of community transmission.

Japan and Korea identified their first confirmed cases at nearly the same time, on January 16, 2020, and January 20, 2020, respectively [10]. Korea subsequently adopted a “3T” strategy—testing, tracing, and treatment—which involved extensive testing of potential cases and their contacts, isolation of individuals who tested positive, and quarantine of exposed individuals who initially tested negative [11]. Although the 3T strategy was widely praised for flattening the initial epidemic curve, it relied on highly intrusive data collection practices that raised privacy concerns [12]. The government mandated the compulsory collection of personal data, including credit card transactions, mobile phone location records, and access logs for public facilities [12].

In contrast, Japan’s policy was often summarized by the “3 Cs” framework, which emphasized avoiding closed spaces, crowded places, and close-contact settings [13]. Rather than implementing a forceful, centrally coordinated response, Japan adopted a largely voluntary, cooperation-based strategy. For case confirmation, polymerase chain reaction (PCR) testing during the early phase of the pandemic was primarily limited to individuals with persistent symptoms or specific risk factors [14]. Consequently, PCR positivity—the proportion of confirmed cases relative to the number of tests performed—was consistently several times higher in Japan than in Korea [10]. For example, at the end of February 2020, the positivity rate was 2.9% in Korea and 16.1% in Japan [10].

Although Japan also operated a contact tracing system, the strictness and operational details of contact tracing differed markedly between Japan and Korea. Scoring systems used to compare public health policies across countries reduce such systems to a binary “present or absent” measure [3], a simplification that can obscure substantial policy differences. In Japan, for example, contact identification relied largely on voluntary disclosure; a national survey indicated that 27.6% of respondents would not fully report all recent contacts [15]. By contrast, contact identification in Korea involved the mandatory collection of personal data, and withholding such information could lead to legal penalties. Therefore, if early public health interventions aimed at suppressing transmission had been the decisive determinant of pandemic outcomes, Japan would have been expected to perform much worse than Korea. Nevertheless, the observed outcomes did not follow this pattern.

COMPARISON OF EXCESS MORTALITY BETWEEN JAPAN AND KOREA

Among the various indices used to evaluate national pandemic responses, excess mortality is widely regarded as the most comprehensive measure because it captures changes in all-cause mortality during the pandemic relative to pre-pandemic levels [16]. In contrast, reported COVID-19 cases and deaths per capita are strongly influenced by national testing policies. Therefore, Japan’s reported COVID-19 case and death counts were underestimated because PCR testing was more limited in Japan than in Korea.

Table 1 summarizes estimates of excess mortality in Japan and Korea reported by different research groups. Excess mortality was calculated using the P-score, defined as observed deaths minus expected deaths, divided by expected deaths. The table includes only studies that examined the full pandemic period from 2020 to 2022 and excludes studies that focused solely on specific phases.

Table 1.

Comparison of excess mortality during the coronavirus disease 2019 (COVID-19) pandemic between Japan and Korea

	Excess mortality (P-score, %)1			Estimation method		Reference
	2020	2021	2022	Statistical model	Reference period
	Japan	−1.7	+2.2	+7.6	Two-stage interrupted time series analysis		2015–2019	[17]
Korea	+0.3	+4.0	+20.7	Age-stratified linear regression	2015–2019	[19]
	+1.5	+4.2	+21.0	Multivariate linear regression	2010–2019	[20]2
	+2.1	+5.6	+19.6	Quasi-Poisson interrupted time-series model	2015–2019	[18]3

¹Excess mortality was expressed as the P-score, defined as (observed deaths−expected deaths)/(expected deaths)×100.

²This study compared a seasonal autoregressive integrated moving average model, a long short-term memory model, and a multivariate linear regression model; The multivariate linear regression model was selected for the final result.

³P-scores were calculated using the numbers of observed and expected deaths presented in Table 1 of the original article; Although excess mortality in 2021 was estimated using data from the full calendar year, the estimates for other years were based on partial periods: excess mortality for 2020 was calculated using deaths from March 1 to December 31, 2020, and excess mortality for 2022 was calculated using deaths from January 1 to June 30, 2022.

For Japan, 1 study meeting these criteria was identified [17], whereas several studies were available for Korea [18–20]. Although the Korean studies used slightly different statistical approaches, their findings were broadly consistent when models accounted for changes in age structure and long-term mortality trends. Overall, Japan’s excess mortality during the pandemic period was actually lower than Korea’s. When excess mortality in Japan and Korea was recalculated using the same statistical method (Supplemental Material 1), the results were highly consistent with those reported in the published articles listed in Table 1. A year-by-year comparison between the countries could provide additional insight.

Excess Mortality in 2020: Pre-vaccination Period

Notably, Japan did not exhibit excess mortality in 2020; rather, the P-score was estimated at −1.7% (Table 1). This observation is consistent with the downward trend in the age-standardized all-cause mortality rate that year [21]. In Korea, excess mortality in 2020 was also minimal, ranging from +0.3% to +2.1% across studies (Table 1). Although the estimates for Korea were slightly higher than the estimate for Japan, both countries appear to have been only minimally affected by COVID-19 in 2020—particularly compared with Western countries—despite their markedly different public health approaches.

Given that Japan has one of the world’s most rapidly aging populations and that COVID-19 mortality risk is disproportionately high among older adults, its negative excess mortality in 2020 is particularly remarkable. During the early phase of the pandemic, Japan’s low fatality numbers despite comparatively loose public health measures were described as the “Japanese paradox” [22]. Several hypotheses have been proposed, including societal and epidemiological factors such as widespread hygiene practices, social customs that limit physical contact, and the country’s relatively low prevalence of obesity. Policy-related explanations have also been discussed, including the government’s clear public messaging encouraging people to avoid the “3 Cs” (closed spaces, crowded places, and close-contact settings) [22]. However, Japan’s most distinctive policy may have been its limited PCR testing strategy, which operated in the opposite direction to other public health approaches aimed at suppressing viral transmission.

In Korea, successful early management of COVID-19 has been attributed to rigorous contact tracing, extensive testing of contacts, and early quarantine measures [23,24]. However, when excess mortality patterns in Japan and Korea during 2020 are compared, these interventions may not appear to have been the primary determinants of Korea’s favorable outcomes. At a minimum, the 2020 excess mortality data challenge the prevailing assumption that public health measures centered on aggressive containment of viral transmission necessarily lead to superior pandemic outcomes.

Excess Mortality in 2021: Active Vaccination Period

The absent or minimal excess mortality observed in both countries in 2020 began to shift in 2021, when excess mortality increased modestly. Japan reported approximately +2.2% excess mortality, whereas Korea reported an excess mortality of approximately +4.0% to +5.6% (Table 1). Japan hosted the Tokyo Olympic Games in summer 2021, after the event had been postponed for 1 year from its originally scheduled start in late July 2020, whereas Korea maintained the 3T strategy. Because increased physical contact within the domestic population and between domestic residents and international participants was inevitable, the event was expected to hinder pandemic control. However, based on excess mortality patterns, its impact appears to have remained minimal in Japan.

In contrast to analyses focused specifically on Japan and Korea, which used slightly different methods to estimate excess mortality, 2 global excess mortality studies covering 2020 and 2021 applied a consistent methodology across countries. At first glance, such cross-national comparisons of excess mortality may appear more valid than the studies cited in Table 1. However, this approach depends heavily on statistical models used to estimate key variables, such as expected mortality, and the resulting estimates may therefore be problematic. Indeed, the 2 global studies produced conflicting findings for Japan and Korea. One analysis reported higher excess mortality in Japan during 2020–2021 [25], whereas the other reported higher excess mortality in Korea [26]. However, the former study was strongly criticized by other researchers for producing implausible estimates across multiple countries, including Japan [27]. For example, expected deaths in 2020–2021 were substantially underestimated relative to pre-pandemic trends, resulting in overestimated excess mortality and raising doubts about the validity of that global analysis. By contrast, the latter assessment was consistent with findings from independent analyses conducted within each country.

Excess Mortality in 2022: Post-vaccination Period

In 2022, after the emergence of the Omicron variant, excess mortality rose sharply in both Japan and Korea, reaching +7.6% and approximately +20.0%, respectively (Table 1). Japan’s increase nevertheless remained roughly one-third of that observed in Korea. This pattern is notable because it emerged during a period when both countries had already achieved high COVID-19 vaccination coverage, at approximately 80% [28]. In addition to high vaccination coverage, face-mask use remained consistently above 90% in both countries during 2022, comparable to the levels reported in 2020 and 2021 [10,29].

Although overall vaccination coverage was similar, Korea’s booster dose uptake at the start of the Omicron wave was substantially higher, largely because of its vaccine passport system. On January 1, 2022, 35.8% of Koreans had received a booster dose, compared with only 0.8% in Japan [28]. If vaccination had been the dominant factors shaping pandemic outcomes, both countries—having achieved similarly high vaccination rates—would have been expected to exhibit comparatively low excess mortality in 2022, as they had in 2020 and 2021. Moreover, Japan’s much lower booster coverage would ordinarily have been expected to correspond with less favorable outcomes, yet the observed pattern differed.

COVID-19 vaccines are well established as highly effective in reducing hospitalization and mortality from COVID-19 [30]. However, the excess mortality patterns observed in 2022 raise important questions about the relative contributions of widespread vaccination and intensive booster campaigns to trends in all-cause mortality. In Japan, continued excess mortality into 2023 has drawn additional attention [31]. Similarly, Korea also experienced continued excess mortality in 2023 (+11.1%), comparable to Japan (+11.3%) (Supplemental Material 1). Although a possible association between repeated COVID-19 vaccination and excess mortality has been suggested in the literature [31], this remains an open question that requires careful, methodologically rigorous investigation of potential underlying mechanisms.

DISCUSSION

In this study, we compared public health policies and pandemic outcomes between Japan and Korea during the COVID-19 pandemic. The similar pattern of excess mortality observed in both countries throughout the pandemic—especially despite their contrasting PCR testing strategies—challenges the view that East Asia’s early success stemmed primarily from stringent virus-suppression measures. This pattern suggests that factors beyond public health interventions may have contributed to the low COVID-19 mortality observed in East Asia in 2020, as discussed below.

Because this study compares only Japan and Korea, concerns may be raised about the generalizability of the findings to all East Asian countries. However, including more than 2 countries would make detailed, context-specific policy comparisons more difficult. As in global comparative studies, a scoring system would likely be required to compare multiple countries; however, such systems capture only simplified representations of policies and risk replacing real-world complexity with numerical convenience. Therefore, our approach—focusing on 2 countries with comparable demographic structures, socioeconomic conditions, and healthcare systems—offers distinct advantages.

Possible Role of Pre-existing Immunity in East Asia’s Early Pandemic Outcomes

Several studies have proposed pre-existing immunity as a potential explanation for the regional differences observed during the COVID-19 pandemic [32,33]. Accordingly, population-level variation in pre-existing immunity may help explain the low COVID-19 mortality observed in East Asia in 2020. This pattern was not limited to Japan and Korea. Many East Asian countries—including Vietnam, Laos, and Cambodia—also reported low COVID-19 mortality and low excess mortality in 2020, despite poorer socioeconomic conditions and healthcare systems than Japan and Korea [10]. This observation further suggests the possible role of underlying biological factors.

Prior exposure to other coronaviruses—including endemic human coronaviruses and severe acute respiratory syndrome coronavirus (SARS-CoV)-1—may have conferred partial cross-reactive immunity to SARS-CoV-2, potentially mediated by adaptive T-cell responses [34,35]. Although such cross-immunity does not necessarily prevent infection, it has been associated with reduced disease severity [36]. Consequently, in settings where testing was limited for asymptomatic or mildly symptomatic infections, populations with higher levels of pre-existing immunity might be expected to exhibit a smaller observable impact of COVID-19. This hypothesis may be consistent with the situation observed in Japan in 2020.

Several lines of evidence support the possibility that pre-existing immunity may have been more common in parts of East Asia. Genetic signatures consistent with ancient coronavirus exposure have been identified in the genomes of East Asian populations, suggesting that coronavirus-like pathogens may have circulated in the region in the distant past [37]. In addition, field studies from Southeast Asia indicate that asymptomatic or mild exposure to unidentified bat-origin coronaviruses may be relatively common [38]. Together, these observations raise the possibility that repeated exposure to diverse coronaviruses or related viruses may be more common in East and Southeast Asia, potentially contributing to a greater degree of immunological preparedness against SARS-CoV-2.

Pre-existing memory T-cell responses also help explain the very low seroprevalence reported in Japan in 2020 [39,40]. Although the markedly higher PCR positivity rate among those tested in Japan than in Korea suggests that community transmission was more widespread in Japan [10], this pattern was not adequately reflected in seroprevalence studies. This apparent discrepancy may be explained by the presence of cross-reactive memory T cells, which have been shown to facilitate rapid viral control following exposure to SARS-CoV-2 [41]. If viral replication is contained early at the site of entry and systemic dissemination is limited, individuals with such immune memory fail to develop detectable antibody responses after exposure; this phenomenon has been consistently observed in clinical studies [41,42]. Collectively, these findings highlight a critical limitation of relying solely on seroprevalence studies to estimate the true extent of community transmission.

Potential Role of Less Restrictive Measures in Shaping Pandemic Outcomes

Japan’s comparatively favorable outcomes relative to Korea raise an additional question: whether allowing a limited degree of viral transmission among lower-risk individuals—without extensive testing and isolation of largely asymptomatic or mildly symptomatic cases—may have contributed to better overall outcomes. In 2020, the concept of focused protection, which emphasizes prioritizing the protection of high-risk populations rather than applying uniformly restrictive measures across society, was met with substantial criticism [43]. This approach has mainly been discussed in the context of reducing collateral societal harms associated with broad lockdowns, including adverse effects on physical and mental health, economic activity, education, and social functioning [44]. However, its potential implications for pandemic control should not be dismissed.

One possible biological rationale is that natural infection, which exposes the immune system to multiple viral epitopes, generate broader immune protection against rapidly evolving viruses such as SARS-CoV-2 than vaccines that target a more limited set of antigens [45]. Supporting this possibility, a meta-analysis of 65 studies across 19 countries found that prior infection was associated with stronger and more durable protection against reinfection than vaccination alone [46]. Prior infection was also associated with a lower risk of severe disease upon subsequent exposure compared with vaccine-induced immunity [46].

From this perspective, the prevailing negative assessment of Sweden’s experience should be reconsidered. Unlike many countries, Sweden did not implement lockdowns and relied largely on voluntary mitigation measures, without mandating mask use [47]. Although Sweden was heavily criticized early in the COVID-19 pandemic, its overall excess mortality was ultimately lower than that of most European countries [48]. While government policies and individual behaviors—such as mask use—differed greatly between Japan and Sweden, both countries shared a key feature: they permitted some degree of community transmission, albeit through different strategies. The relatively favorable outcomes observed in these settings suggest that the potential role of viral transmission among lower-risk populations warrants further examination as a factor that may have influenced overall pandemic outcomes.

Nevertheless, comparisons among the Nordic countries showed excess mortality in Sweden in 2020, whereas other Nordic countries experienced excess mortality in 2021 or 2022 [49,50]. This pattern may indicate that Sweden experienced a disadvantage in terms of person-years of life lost. However, the elevated excess mortality observed in Sweden in 2020 should be interpreted considering the unusually low number of deaths observed in 2019 [51]. Consequently, a larger pool of vulnerable older adults had accumulated by March 2020, contributing to higher mortality during the early phase of the COVID-19 pandemic—a phenomenon often referred to as the “dry tinder effect” [52].

CONCLUSION

To date, the relatively favorable pandemic outcomes observed in East Asian countries have been attributed to early public health interventions aimed at suppressing viral transmission. Large-scale early testing, in particular, has frequently been cited as a key factor in Korea’s apparent early achievements during the pre-Omicron period. However, the comparison between Japan and Korea does not support this widely accepted interpretation. Other factors—such as the possible contribution of higher levels of pre-existing immunity in the region—deserve closer examination.

In this context, Korea’s aggressive 3T strategy—which required substantial resources and raised serious privacy concerns—warrants reconsideration. Although public health strategies should reflect pathogen characteristics, policies aimed at protecting high-risk populations may have particular merit for diseases such as COVID-19. For this purpose, prioritizing PCR testing for high-risk populations, rather than implementing mass testing, could represent a more efficient approach. Furthermore, the potential role of pre-existing immunity highlights the need for geographically tailored approaches, rather than the assumption that a single strategy is universally optimal. Supporting our critique of public health measures that became widely accepted during COVID-19, a recent review highlighted the limitations of both non-pharmaceutical and pharmaceutical interventions [53]. Collectively, these findings suggest that many current pandemic response strategies should be thoroughly reevaluated.

Supplemental Materials

Supplemental material is available at https://doi.org/10.3961/jpmph.26.274.

Supplemental Material 1.

Comparison of excess mortality* during the COVID-19 pandemic between Japan and Korea