Variables and Terms

Data Analysis

This study aims to analyze the transmission dynamics, health care burden, and combined effects of SI, vaccination, and viral variants on COVID-19 indicators across 6 countries. Statistical analyses were conducted via R software (version 4.4.1). For continuous variables, normality tests indicated a departure from a normal distribution in most cases; thus, these variables were summarized using medians and interquartile ranges (IQRs). Group comparisons of continuous variables were performed via the Kruskal–Wallis test. Regression analyses employed both univariate and multivariate generalized linear models (GLMs) to assess the relationships between the SI and vaccination with outcomes such as hospital admissions, ICU occupancy, and excess mortality. Model 1 represents an unadjusted model, whereas Model 2 adjusts for either the SI or vaccination status.

To handle missing values in the raw data, linear interpolation was applied when the proportion of missing data was less than 20%; records with more than 50% missing data were excluded from the analysis. Additionally, data on variant proportions were merged with the primary indicators by date and country to create a comprehensive dataset. The monthly proportions of major variants (e.g., Alpha, Delta, Omicron BA.1, and BA.5) were included as variables.

Discussions

To explore the diverse outcomes of national COVID-19 responses, this study examines how differences in restrictive policies, vaccination coverage, and predominant circulating SARS-CoV-2 variants across 6 countries are associated with variations in infection rates, excess mortality, hospitalization rates, and ICU occupancy. The USA and the UK represent Western developed nations with advanced health care systems, although policy implementation varies due to federal structures and political divergences, while China’s stringent “zero-COVID” policy exemplified centralized governance. Russia and South Africa, representing transitional and developing economies, encountered resource constraints, and Japan’s efficient public health system showcased moderate, adaptive measures. To better understand the governance logic and outcome differences behind national pandemic policies, this study adopts the adaptive leadership framework proposed by Heifetz and Northouse, which emphasizes collaboration, flexibility, and stakeholder empowerment over hierarchical command-and-control models. ^{Reference Heifetz, Grashow and Linsky13,Reference Northouse14} Using this framework, the study explores the role of adaptive leadership across the preparedness, response, and recovery stages of the pandemic, with the aim of providing both theoretical insights and practical guidance for future public health crisis management.

In the preparedness phase of a pandemic, adaptive leadership emphasizes proactive monitoring of global health trends, identifying vulnerabilities in public health infrastructure, and promoting the establishment of cross-sectoral collaboration mechanisms.Reference Powell, Orttung and Topkok ¹⁵ Inadequate investment in public health infrastructure in the USA, longstanding health inequities, and socioeconomic factors exacerbate the USA’s vulnerability to the pandemic.Reference Maani and Galea ¹⁶ Additionally, the decentralized nature of the USA response led to substantial policy variations across states, with the federal government prioritizing economic support and research funding over a unified testing and population surveillance system.Reference Bergquist, Otten and Sarich ¹⁷ This partly explains the phenomenon observed in our data, where the USA ranks among the highest in both infection and death rates. Similarly, globally, health care systems faced immense pressure during the pandemic, as the surge in demand for inpatient and outpatient care exacerbated resource shortages and inadequate patient care coverage.Reference Cohen, Pignata and Bezak ¹⁸ Take the UK as an example. Its high total number of infections and mortality rate may be influenced by a combination of the following factors: limited early vaccination coverage, an aging population (93% of deaths occur among people over 60 years old), and tight medical resources.Reference Brown, Heinsbroek and Kall ¹⁹ These circumstances collectively highlight the urgent need to strengthen public health infrastructure, promote cross-sectoral collaboration, and develop coordinated and consistent response strategies. Compared with other countries, Japan achieved a Healthcare Access and Quality (HAQ) Index score of 94 out of 100, ranking 12th globally. With 13.2 hospital beds per 1,000 people, ²⁰ its efficient health care system and strong public health response capacity partly explain the relatively high ICU occupancy and low excess mortality. Japan’s experience serves as a model for the importance of proactive investment, cross-sectoral collaboration, and systematic preparedness in crisis governance. It highlights the value of establishing robust infrastructure and multi-agency coordination mechanisms before a crisis occurs.

At the same time, adaptive leadership emphasizes adjusting strategies in response to environmental changes to address evolving challenges.Reference Laur, Agarwal and Mukerji ²¹ For example, vaccine development and deployment played a central role in the response to COVID-19, demonstrating a high level of global scientific collaboration and organizational adaptability. Several countries completed vaccine development and obtained emergency use authorization within an exceptionally short timeframe, providing a crucial intervention to reduce the risks of severe illness and mortality.Reference Mohammed, Nauman and Paul ²² The unadjusted models in this study show a significant negative correlation between vaccination rates and the number of hospitalized and ICU patients in the USA and South Africa, indicating that vaccines effectively reduced the burden on health care systems, consistent with their expected protective effects. However, the protective effect of vaccines wanes over time. For instance, 25 weeks after receiving 2 doses of ChAdOx1, BNT162b2, or mRNA-1273 vaccines, protection against symptomatic disease caused by the Delta variant remains at 40-80%, but drops below 20% for the Omicron variant.Reference Andrews, Stowe and Kirsebom ²³ This dynamic process highlights the critical role of adaptive leadership in public health responses. Especially in the face of viral mutations and immune evasion, organizations must continuously adjust their strategies and strengthen efforts in vaccine updates and booster promotion to ensure sustained protection and systemic resilience.Reference Branch-Elliman, Elwy and Chambers ²⁴ Moreover, adaptive leadership also places strong emphasis on crisis communication and public trust. Recent applications of situational crisis communication theory suggest that insufficient transparency or delayed information can significantly undermine public cooperation.Reference Gallotti, Valle and Castaldo ²⁵ Therefore, establishing communication mechanisms that are transparent, timely, and trustworthy is essential for enhancing system resilience and public responsiveness—making it a core element of effective public health governance.

During the response phase of the COVID-19 pandemic, governments’ ability to adapt policies flexibly and balance centralized and decentralized decision-making directly influenced their capacity to withstand the crisis and adapt strategically.Reference Janssen and van der Voort ²⁶ Our data show that China’s SI was significantly negatively associated with the number of new infections and excess deaths, reflecting to some extent the effectiveness of the command-and-control governance structure in the early stages of the pandemic. By implementing grid-based control strategies—such as citywide lockdowns, household screenings, and centralized quarantines—China was able to curb virus transmission effectively in the short term.Reference Wei, Ye and Cui ²⁷ This experience underscores the potential advantages of centralized coordination and rapid response in pandemic control, offering valuable insights for understanding epidemic trajectories and evaluating the effectiveness of intervention measures. In contrast, Japan’s COVID-19 response relied on voluntary restrictions and stringent border controls, avoiding mandatory lockdowns.Reference Kodama, Campbell and Tanaka ²⁸ The effectiveness of its response was supported by high levels of public cooperation, a cultural emphasis on collective responsibility, and widespread adherence to protective measures such as mask-wearing. ^{Reference Kodama, Campbell and Tanaka28,Reference Song and Karako29} This aligns with Heifetz’s concept of “giving the work back to the people,” where local communities are empowered with autonomy and collaborate with an efficient public health system to flexibly address pandemic challenges.Reference Heifetz, Grashow and Linsky ¹³ Our data also indicated that Japan recorded the lowest excess mortality rate among the compared countries (−2 per 100,000), reflecting the effectiveness of its strategy.

The continuous evolution of the virus has made ongoing surveillance of its variants especially critical. Studies indicate that the Alpha, Beta, Gamma, Delta, and Omicron variants exhibit greater transmissibility and potentially higher pathogenicity than the wild-type strain does.Reference Chakraborty, Sharma and Bhattacharya ³⁰ Our data further indicate that between mid-2020 and mid-2021, the Alpha and Delta variants became the dominant strains in the USA and the UK, significantly contributing to increased hospitalization and ICU admission rates. Since late 2021, Omicron has demonstrated a 10-20% higher transmission rate than the Delta variant, along with notable immune escape potential.Reference Fan, Li and Zhang ³¹ Under its influence, the hospitalization rate in the USA rose to approximately 400 cases per million people, with similar rebounds observed in the United Kingdom, Japan, and South Africa.

During the response phase of pandemic control, challenges arising from social factors are equally significant. The effectiveness of response efforts largely depends on the actual implementation of policies and the level of public compliance. In Western countries, some individuals resist preventive measures because of cultural beliefs (e.g., viewing masks as restrictions on personal freedom) or religious convictions. ^{Reference Chen and Biswas32,Reference Duarte, Moro and Ferreira da Silva33} In China, population demographics influence compliance, with middle-aged individuals showing greater adherence to mask-wearing and temperature checks but lower compliance with household isolation.Reference Xu, Chew and Xu ³⁴ Notably, Japan achieved effective epidemic control despite maintaining a relatively low SI, likely due to high levels of self-discipline and public adherence to health measures. This underscores the vital role of public cooperation in policy execution and aligns with the view proposed by Yukl and colleagues that trust plays a critical role in enhancing organizational adaptability and response effectiveness.Reference Chen and Sriphon ³⁵

Vaccination has played a critical role in controlling the COVID-19 pandemic, yet its rollout has faced numerous social and economic challenges. According to the USA Centers for Disease Control and Prevention (CDC), global vaccine distribution inequities have posed challenges for low-income countries, driven by supply shortages, logistical barriers, and public vaccine hesitancy.Reference Zibadi, Samieefar and Sodeifian ³⁶ Differences in national vaccination strategies have further influenced the effectiveness of pandemic control. In China, high vaccination coverage combined with strict nonpharmaceutical interventions created a dual protection mechanism that effectively reduced the infection rate and excessive mortality rate. In contrast, South Africa’s vaccination coverage was lower, primarily constrained by limited vaccine access, challenges in cold-chain logistics, and public concerns over vaccine safety, potentially leading to insufficient protection against viral variants and increasing risks of severe illness and mortality. ^{Reference Cooper, van Rooyen and Wiysonge37,Reference Kahn, Pettifor and Mataboge38} Furthermore, studies have reported rare adverse effects associated with vaccination, such as myocarditis, immune thrombocytopenia (ITP), and autoimmune hepatitis, which have heightened public concerns about vaccine safety, potentially indirectly affecting vaccination uptake and pandemic control outcomes. ^{Reference Hines, Shen and Olazagasti39–Reference Zhou and Ye41}

In the recovery stage, analyzing long-term health (e.g., long COVID-19), economic (e.g., unemployment), and social (e.g., mental health) impacts was crucial. ^{Reference McDaid42,Reference Vartanian, Fish and Kenton43} China’s command-and-control model was effective in curbing virus transmission during the initial phase of the outbreak; however, this highly centralized crisis response approach also brought certain negative consequences. On one hand, prioritizing a vast amount of resources for COVID-19 control may have led to the neglect of other routine health care needs, thereby increasing the risk of non-COVID-related mortality. Our findings align with existing research suggesting that resources in centralized crisis responses are often allocated reactively rather than proactively.Reference Silva, Souza and Roquete ⁴⁴ On the other hand, prolonged implementation of stringent measures (e.g., lockdowns, mandatory isolation) may adversely impact the mental health of vulnerable groups (such as children, women, and the elderly), as well as economic stability, education, and food security, ^{Reference O’Connor, Wetherall and Cleare45,Reference Onyeaka, Anumudu and Al-Sharify46} potentially leading to unsustainable policy enforcement. This aligns closely with organizational behavior research on “policy fatigue,” reflecting considerations in disaster leadership regarding the balance between action and social costs.Reference Harvey ⁴⁷ The supplemental data (Table S1) indicate that, except for China, the SI in other countries declined in 2021, reflecting a shift away from prolonged high-pressure control strategies. In this context, introducing the concept of adaptive leadership can help address the limitations of the traditional command-and-control model by enhancing the flexibility and sustainability of pandemic policies.

The unequal distribution of resources during the recovery phase has further widened disparities between countries and population groups. The surge in hospitalization demand, export restrictions on personal protective equipment, and disruptions in global supply chains during the pandemic collectively strained medical resources worldwide.Reference Yin, Song and Wang ⁴⁸ In resource-limited settings such as South Africa, these shortages further weakened the effectiveness of containment measures and increased mortality risks. Such resource constraints not only reflect the disparities in public health capacity between nations but also highlight a fundamental challenge in disaster response—how to achieve equitable and efficient resource allocation during crises.Reference Garavaglia, Sancino and Trivellato ⁴⁹ Therefore, ensuring fairness in resource distribution—particularly by supporting regions with weak health care systems—will be a critical step toward achieving sustainable global public health security in the post-pandemic recovery.

As summarized in Table 4, adaptive leadership played distinctive roles during different pandemic stages. Cross-national variations in vaccination coverage and policy stringency underscore the critical value of adaptive leadership in resource coordination and responsiveness to societal feedback. China established a dual defense mechanism by combining high vaccination rates with strict lockdowns, while South Africa, constrained by logistical and resource limitations, experienced insufficient vaccine coverage. In the USA, the federal system led to inconsistent containment strategies and uneven vaccine rollout progress. Vaccine hesitancy and a lack of public trust also hindered the response in several countries, highlighting the importance of community engagement and transparent communication. Japan achieved low infection rates through voluntary restrictions, exemplifying an adaptive governance approach rooted in social empowerment. However, the prolonged use of high-intensity measures also led to “policy fatigue,” with adverse effects on mental health and socioeconomic stability. These cases illustrate that adaptive strategies must be tailored to specific contexts and evolving conditions, while also maintaining a dynamic balance between the effectiveness of interventions and their social costs—an essential condition for building a more resilient system of public health governance.

Table 4.

Role of adaptive leadership in COVID-19 pandemic stages

Despite providing insights into the COVID-19 response strategies and their outcomes across six countries, this study has several limitations that may affect the interpretation and generalizability of the findings. First, the study primarily relies on data from the “Our World in Data” database, which may be subject to reporting biases. Variations in case definitions, testing capacities, and mortality reporting standards across countries may compromise the comparability of the data. The previous study has demonstrated substantial underreporting and undertesting in several countries, including France, Spain, and Italy.Reference Lau, Khosrawipour and Kocbach ⁵⁰ Second, due to data availability constraints, the study did not fully adjust for confounding factors, such as environmental conditions, population density, health care infrastructure, and public trust in government. These factors may influence the effectiveness of public health interventions. Third, the SI, used as a measure of policy intensity, has intrinsic limitations. It is derived solely from the formal content of policy documents and does not account for the actual level of enforcement or public compliance. Future research should aim to reduce reporting bias through multi-source data validation, such as hospital records, serological surveys, control for confounding factors using multivariate analysis, and incorporate measures of policy implementation and public compliance. Extending the study period could help capture long-term trends of public health interventions.