Public health emergencies, defining as much by their triggering events as by their health consequences (1), profoundly impact social systems, policies, and health. The health consequences of public health emergencies possess the potential to exceed the routine capabilities of the community, characterized by a scale, timing, or unpredictability that poses a significant threat to the existing response capacity (2). With the raise of interaction between nature and human actions, emerging viral zoonoses are a critical threat to public health (3). Historical analysis reveals several paradigmatic examples of such emergencies. The 1918–1919 H1N1 influenza pandemic resulted in the death of approximately 50 million people worldwide, accounting for 3–5% of the global population at that time. It tremendous pressure on public health systems, medical resources, and social life (4). Another prominent example emerged in 2002–2003 with the global outbreak of severe acute respiratory syndrome (SARS), which resulted in 8,098 confirmed infections and 774 deaths, yielding a case fatality rate of 9.60% (5). In December 2019, COVID-19 caused a global pandemic that resulted in more than 6.5 million deaths (6). The World Health Organization (WHO) declared the COVID-19 outbreak an international public health emergency on January 30, 2020 (7). As the most significant public health event in recent years, it has profoundly impacted mental health (8).

The COVID-19 pandemic has triggered a wide range of mental health symptoms across different populations, with significant disparities observed globally. Large-scale international studies have begun to systematically assess these impacts. An international study administered in 30 countries across the globe assessing the health-related impacts of the COVID-19 pandemic on individuals’ fear of the pandemic examined its global effects on lifestyle behaviors, fear, depression, and perceived community needs (9). A cross-sectional study focused on fear in general populations on perceived fear of common diseases, life events, and environmental threats in 30 countries (10). Furthermore, the mental health disparities among the general public caused by COVID-19 have been documented by many scholars. A network analysis of a large international observational study figured that, quality of life, emotional distress, and the overall amount of exercise are key intervention components for improving overall lifestyle, overall health and overall health via lifestyle in the general population, respectively (11). Comparative studies reveal that mental health burdens varied significantly across countries, often influenced by economic and epidemic severity factors. Li et al. (12) assessed and made cross-country and cross-region comparisons of the global impacts of COVID-19 and preparation preferences of pandemic. Countries with a high-income level or medium to high COVID-19 severity reported higher perceived mental burden and emotional distress. In Slovenia, the risk of depression, anxiety, and stress was well controlled during the first wave of COVID-19 when the daily record of positive cases was only 61 and the healthcare system was not overwhelmed, but it was not well controlled during the second wave (the epidemic was again announced on 18 October 2020) when infections spread rapidly and exponentially, strict measures were prolonged, and Slovenia became one of the hardest-hit countries (13). In Brazil, where the pandemic emerged amid political and scientific conflict, a survey conducted from May 22 to June 5, 2020, 5 months after the first confirmed case, found a high prevalence of depression (46.4%), anxiety (39.7%), and stress (42.2%) (14). Around the same period, in Malaysia, during the conditional movement control order (CMCO) from 13 May to 9 June 2020 followed by a more lenient recovery movement control order (RMCO) from 10 June to 31 August and extended until 31 December, there were increased depressive, anxiety, and stress symptoms from 12 May to 5 September 2020, with depression showing the greatest rise (15). Overall, these findings highlight that the prevalence and trajectory of depression, anxiety, and stress during the COVID-19 pandemic varied across countries, reflecting differences in pandemic severity, public health measures, and socio-political contexts.

It is evident that, there are significant differences in the prevalence of depression and anxiety among different countries, and the prevalence of depression and anxiety during the same period are also different. These differences are not only attributable to the timing and severity of the outbreak but are also influenced by factors such as age, gender, occupation, lockdown policies, race, and other demographic variables.

A substantial number of social theories pertaining to health have been employed to elucidate the phenomenon of variability in the public’s mental health that have emerged as a consequence of the COVID-19 pandemic. Some scholars explore this issue from the perspective of social stratification theories. Their studies reported that the scale of a society’s income inequality is a determinant of population health (16). Social factors such as socioeconomic status and social support are likely posited as “fundamental causes” of disease. These factors, by virtue of their embodiment of access to critical resources, exert influence on multiple disease outcomes through diverse mechanisms (17). The structural determinism view is that, systemic power structures such as racism and sexism indirectly harm the health of vulnerable groups through institutional exclusion (18). For people of color, the systemic and structural racism produce, condone, and perpetuate widespread unfair treatment and oppression of them, with adverse health consequences (19). Social capital theory hold the view that differences in trust, reciprocity, and resource flow in social networks such as strong or weak community cohesion affect the health level of the group (20).

Given the multifaceted ways such as those rooted in socioeconomic status and systemic power structures, influence health outcomes, it is imperative to adopt a more comprehensive perspective to understand and address the public mental health exacerbated by the COVID-19 pandemic (18–20). The model of social determinants of health (SDH) was first presented by the scholars Dahlgren and Whitehead in 1991 (21). In 2008, the WHO Commission on Social Determinants of Health further elaborated the definition in its report Closing the Gap in a Generation. WHO defines SDH as “the conditions in which people are born, grow, live, work and age,” conditions or circumstances that are shaped by families and communities and by the distribution of money, power, and resources at global, national, and local levels and affected by policy choices at each of these levels (22). Individual and group-level social determinants include gender, race, social class, education, income, occupation, employment status, housing tenure, immigration status, disability status, and social capital. Population-level determinants encompass health service provision, access to essential services, medically underserved or health professional shortage areas, and public expenditures on safety, social, and welfare services (23).

To date of research, there has been a lack of systematic reviews that summarized the impact and manifestations of depressive and anxiety symptoms among the general population during disease outbreaks, particularly exemplified by COVID-19, across countries with varying levels of development. To better understand the social structural roots of mental health inequalities across countries with different levels of economic development, this study was framed within SDH. Focusing on three dimensions: individual social determinants, population-level determinants and community-level social support determinants, this research deepens the theoretical understanding of health inequalities, particularly revealing how social structures in health emergencies shape mental health differences, offering a new perspective for cross-national comparative studies in sociology and public health.

The results of this systematic review underscored the profound global impact of the COVID-19 pandemic on mental health, with significant variability across countries, demographics, and policy responses. The findings reveal that the prevalence of depression and anxiety increased during the pandemic, with younger individuals (28, 36, 37, 39, 40, 42, 63), females (32, 39, 63), and socioeconomically disadvantaged groups disproportionately affected (30, 43, 45). Population-level factors, such as healthcare infrastructure (49, 52, 64, 65) and policy stringency (57, 64, 65), played crucial roles in shaping mental health outcomes. Stricter lockdowns often led to elevated psychological distress (15, 55, 57, 66), particularly in low-resource settings (52), underscoring systemic health inequalities.

Temporal patterns also emerged, highlighting how mental health outcomes fluctuated during different pandemic waves. Countries with effective early containment strategies, like China, saw improvements in mental health over time (67), while prolonged lockdowns in places like France and Slovenia correlated with worsening outcomes (13, 29). Lower-income individuals faced heightened mental health challenges (43, 45, 68), and higher educational levels correlated with distinct stress responses (31, 48, 49). Educational disparities underscored varied vulnerabilities based on knowledge and perceptions of the pandemic (31). Moreover, reduced social support significantly exacerbated depression and anxiety symptoms, emphasizing the protective role of marital status and community bonds (61, 68, 69).

The COVID-19 pandemic has profoundly affected mental health globally, with significant disparities influenced by demographic, socioeconomic, and national policy factors. These factors will act synergistically by influencing core elements such as economic livelihood security, thus forming the risk characteristics of mental health in specific groups. Some groups of the population may be more vulnerable to detrimental effects of the pandemic on mental health than others. Vulnerable populations, such as younger individuals, women, and those with lower socioeconomic status, experienced heightened levels of anxiety and depression. The work environment, and social networks showed the importance of personal factors for their mental health risk-and protection (70). Greater societal determinants of health inequality impacts their risk for disparate healthcare access and outcomes (71). Besides mental health, vulnerable populations are also at risk of poor psychological and social health underlying this definition of vulnerability is the epidemiological concept of risk. Community and associated individual characteristics are risk factors that encompass those attributes or exposures related or lead to increases in the probability of occurrence of health-related outcomes (72). These vulnerable populations will face greater risk when it comes to health outcomes beyond depression and anxiety.

The core issue of depression and anxiety stems from the lack of financial security caused by low income. The relationship between poverty and mental illness is a bidirectional causal, and the resulting concerns and uncertainties could exacerbate mental health issues (73). Factors such as age, income, living situation, and isolation can all trigger emotional issues in these specific groups, hindering their ability to maintain stable employment. As economic recessions have a context-dependent negative impact on mental health disorders (74). Young people are more likely to perceive emotional stress in sudden situations due to relatively worse psychological resilience and unstable jobs with correspondingly lower income levels. Varma et al. (75), through a global cross-sectional survey conducted in 60 countries, confirmed that younger age-groups were more vulnerable to adverse mental health outcomes. Factors such as poor sleep quality, loneliness, resilience and age emerged as mediators in the relationship between stress and mental health, highlighting these as potential targets for interventions. Kinship-loss affected population and those who are homeless are more susceptible to the impact due to their already precarious economic foundation and psychological makeup. Similarly, with underlying conditions such as emotional disorders or a history of pneumonia-related illnesses are also more likely to experience a dual impact of physiological and psychological distress. Inversely, various mental illnesses also increase the risk of multiple chronic physical diseases (76), which foreshadows the bidirectional importance and necessity of mental health practice interventions. Women, in general, due to their relatively weaker psychological endurance, tend to exhibit more pronounced fluctuations in emotional health (77), exacerbated by the additional burden of household division of labor in the role of family caregivers, intensifying the sense of crisis. The different levels of SDH often interact rather than affect independently. Young women and low-income service industry workers face compounding risks suggesting the interplay of social roles and resource scarcity.

Temporal trends and regional differences underscore the role of effective containment measures and social support in mitigating mental health challenges. Local regulations determine the state of contraction in a country or region, and corresponding lockdown policies that are either relaxed or overly strict will present different consequences, which are also related the duration. Meanwhile, these COVID-19 policies or measures are related to the economic development, and the impacts including medical, mental health and other all aspects of daily life. A full shutdown of “nonessential” activities puts market production about 25% below normal in the short run, and it also lead to employment decline (78). During the pandemic, the utilization of medical services can be reduced by nearly one third, with significant variability, and a greater reduction for less severe disease populations (79).

The interrelatedness among social groups has a significant impact on the emotional state of the population during sudden public health emergencies. Social support can stabilize emotions, and its consequences were subsumed under the general rubric of positive health states (78). The population that has been forcibly quarantined lacks interaction with the outside world, and the group of young people living alone experiences a more sense of loneliness. Reducing contact with the outside world and being exposed to more negative online news in this environment of a sudden public health emergencies can more easily lead to emotional issues. Members of the family who have lost loved ones or have family members who are ill with infections, or who face higher infection risks due to their profession, such being frontline medical staff or having family members who are, can also have a more significant impact on their emotions. However, certain studies have also demonstrated that frontline medical personnel with greater medical knowledge tend to respond to the pandemic more calmly (42) as their knowledge, cognition, and perspectives on the pandemic all play a role (31), which could also be a result of the interaction between first-level factors such as personal education level and occupational type. A certain proportion of individuals with higher educational qualifications are able to work on the frontline. These groups experience less unemployment crisis turmoil during public crisis and even gain more economic security, which responds to reduce the sense of crisis in life.

The explanatory power of SDH framework extends beyond documenting health inequalities to providing theoretically grounded guidance for designing disparity-reducing public health intervention strategies. Social-ecological model (SEM) and SDH are similar in their hierarchical classification. The social-ecological model, consisting of five levels of intervention (individual, interpersonal, organizational, community, and public policy), has been effectively in public health practice to influence behavior change and positively impact health outcomes (80). The findings emphasize the need for tailored mental health interventions that account for regional, cultural, and demographic nuances. Public health policies should prioritize vulnerable groups, such as low-income individuals and younger adults, by enhancing access to mental health services and providing targeted support programs. Ecological models of human interaction are often used to study the complex community issues that affect health inequalities (81). In epidemiology, an ecological framework is used to examine a disease as the result of disease or wellness is caused by an interaction between various factors. Structural determinants operate as root causes across ecological levels. Future interventions could adopt a structural-ecological approach, simultaneously targeting policy-level SDH levers and community-level SEM strategies, while employing ecological epidemiology to evaluate multi-factorial interactions. The review also calls attention to the importance of balancing infection control measures with strategies to mitigate psychological harm, such as promoting social support networks and providing clear communication during crises.

This study has several limitations. First, we acknowledge the complexities and lack of consensus in classifying SDH and demographic factors, including the issue of the mutual exclusivity these determinants (82). For example, we categorized housing tenure and disability status as demographic factors, acknowledging their potential classification as community-level factors considering their significant correlation socio-economic conditions. Immigration status and social capital, while categorized as community-level determinants due to their association with social policies, remain subject to disaggregation into population-level determinants. Secondly, the heterogeneity in study designs and measurement tools poses challenges for direct comparison of results. Thirdly, the reliance on self-reported measures of mental health may introduce biases, such as underreporting of symptoms. Additionally, the exclusion of non-peer-reviewed literature might have limited insights into rapidly evolving pandemic-related mental health issues.

Subgroup Considerations and Heterogeneity. Although a meta-analysis was not conducted due to the substantial methodological and contextual heterogeneity across studies, several subgroup patterns emerge from the included literature that merit highlighting. Geographically, studies from high-income countries (HICs) such as the U.S. and France frequently reported sustained psychological distress linked to prolonged lockdowns, whereas nations with early and effective containment strategies—such as China and Italy—exhibited improvements in mental health over time. Temporally, mental health outcomes fluctuated significantly across pandemic waves; for instance, Slovenia showed efficient control during the initial wave but experienced pronounced deterioration in the second wave. Methodologically, variations in measurement tools (e.g., PHQ-9, GAD-7, DASS-21) and sampling strategies (online surveys vs. population-based assessments) introduced additional layers of heterogeneity. Online studies, while necessary during lockdowns, may over represent certain demographics and underrepresent vulnerable groups with limited digital access. These subgroup differences underline the importance of contextual interpretation and caution against overgeneralization of findings. Future reviews may benefit from stratified analyses by region, income level, or pandemic phase to further elucidate disparities and contextual modifiers.

Future studies should direct greater attention toward understudied populations, such as healthcare workers and marginalized communities, to inform the development of inclusive and equitable mental health frameworks. Emphasizing the analytical role of SDH public health and disease epidemiology, further exploring the rich connotation levels and their interrelated relationships. Furthermore, more longitudinal designs should be employed to comprehensively assess the long-term psychological impacts of the pandemic. Encourage comparative studies examining the efficacy of different mental health interventions globally. Comparative analyses of policy interventions across countries could provide critical insights for managing future public health emergencies.

These findings highlight the urgent need for tailored mental health interventions and policies that address systemic inequalities and prioritize resilience-building for at-risk groups. Future research should focus on the long-term impacts of the pandemic, explore effective interventions across diverse populations, and refine strategies to foster global mental health equity.