Under-5 mortality of infectious diseases in 204 countries between 1990 and 2021

Introduction

The under-5 mortality rate (U5MR) is a critical metric for assessing improvements in overall population health and development (1,2). The United Nations adopted the Sustainable Development Goals in 2015, one of which is to end preventable deaths of newborns and children under 5 years of age by 2030 (3). The Sustainable Development Goals further called for eradicating the epidemics of human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS), tuberculosis, malaria, and neglected tropical diseases, while combating hepatitis, water-borne diseases, and other communicable diseases (4,5).

Infections are major contributors to under-5 deaths worldwide (4,6,7). The global number of deaths among children under 5 years of age was 5.3 million in 2019, nearly half of which were attributable to infections (8). The implementation of the integrated Global Action Plan for Prevention and Control of Pneumonia and Diarrhoea, which mainly encompassed universal immunization, promotion of exclusive breastfeeding, antiretroviral prophylaxis, and household air pollution control, has led to significant reductions in U5MR of lower respiratory infections and diarrheal diseases, particularly in low- and middle-income countries (9,10). Meanwhile, there has been a 30–50% decline in the global mortality rate in malaria, and a more than 50% decline in measles among young children from 2000 to 2019 (8). The slower decline in neonatal mortality is attributable to factors beyond infections, including health system-related issues—such as preterm birth complications and birth asphyxia—and maternal health conditions like pregnancy-induced hypertension, all of which contribute to preventable deaths. However, existing data only provide the trends in mortality for several common childhood infections. There is a need for detailed mortality profiles and trajectories and updated information on U5MR for total and specific infections. Changes in the contributions of various infectious diseases to U5MR, as well as the projected trends in mortality for pediatric infections, remain to be clarified.

In this study, we utilized the Institute of Health Metrics and Evaluation (IHME) Global Burden of Disease Study (GBD) 2021 data for a comprehensive analysis of trends in U5MR due to overall and specific infectious diseases between 1990 and 2021. We also forecasted the trajectory of under-5 mortality from infections over the next three decades. The findings may assist in the development of tailored intervention and management strategies in tackling infectious disease burdens in diverse regional populations for optimizing child well-being. We present this article in accordance with the GATHER reporting checklist (available at https://tp.amegroups.com/article/view/10.21037/tp-2026-1-0064/rc) (11).

Methods

Overview

In the present study, we used the data from the GBD 2021, an extensive dataset comprising 371 distinct causes of diseases and injuries. The analysis was conducted using a Bayesian meta-regression tool, DisMod-MR 2.1, the methodology of which has been detailed elsewhere (12). The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments.

Data collection

Data were accessed via the GBD 2021 Data Input Sources Tool on the Global Health Data Exchange (GHDx) (https://ghdx.healthdata.org/gbd-2021/sources). Data for all infectious diseases were obtained and presented as absolute numbers and rates per 100,000 population for two key measures: deaths and disability-adjusted life-years (DALYs). Metrics were expressed as means with 95% uncertainty intervals (UIs). We extracted the data covering five age subgroups (<28 days, 1–5 months, 6–11 months, 12–23 months, 2–4 years), stratified by gender, across 204 countries and territories from 1990 to 2021. Given that the GBD study attributes each death to a single, mutually exclusive cause (13), we pooled the mortality numbers and rates for all infectious diseases of interest to evaluate the disease burdens attributable to the overall and some specific infections with relatively high frequencies.

Definitions

This investigation focused on outcomes for three pivotal target child populations: young children (<5 years), infants (<1 year), and neonates (<28 days). We incorporated cause-specific mortality data for 38 infectious diseases, all of which are preventable as mentioned in Sustainable Development Goal 3.2 (4). They were further categorized into six types, including HIV/AIDS and sexually transmitted infections, respiratory infections and tuberculosis, enteric infections, neglected tropical diseases and malaria, neonatal infections, and other infectious diseases. Except for neonatal sepsis and other infections (classified at level 4), all causes are categorized at level 3, providing enough detailed classification for assignment to major cause groups. The specific diseases included in each category are detailed in Table S1. Furthermore, the IHME calculates the socio-demographic index (SDI) for each country based on the geometric mean of lag-distributed income per capita, average education level (in subjects age 15+ years), and total fertility rate (in females younger than 25 years) (5). This index serves as a comprehensive measure of development status, which correlates significantly with health outcomes.

Statistical analysis

We computed the estimated annual percentage change (EAPC) among children under 5 years of age to characterize the average annual change in disease burden across a specific time frame (14). We utilized locally estimated scatterplot smoothing (LOESS) regression to evaluate the relationship between mortality rate of infectious diseases and SDI across 21 regions (13). The Spearman correlation analysis was performed to calculate the correlation coefficients for examining the strength of the associations between mortality rates and SDI.

Drawing on the concept of population attributable fraction (PAF) (15,16), we quantified the variations between 1990 and 2021 in the contributions of different infectious diseases to the total burden of U5MR and predicted trends in the current decade (2021–2030). A negative value indicated an increase in mortality risk without effective control compared to the initial year, whereas a positive value signifies a successful implementation of an intervention to reduce a death rate. We employed Bayesian Age-Period-Cohort (BAPC) model to forecast the trends in the disease burden among children aged <5 years between 2022 to 2050 (17,18). The BAPC model offers a robust framework for projections, using the Integrated Nested Laplace Approximation (INLA) method for comprehensive Bayesian inference. This approach enables the dynamic integration of age, period, and cohort effects, which are presumed to evolve continuously over time. The effects are smoothed using a second-order random walk (RW2) method, leading to more precise posterior probability predictions for long-term disease burdens.

All statistical analyses and data visualizations were performed using R Studio software (version 4.4.1). The threshold of statistical significance was set at 5%, employing a two-tailed test. Additional details on the methodology can be found in Supplementary Methods.

Results

Global trends

In 2021, infectious diseases were responsible for 2.0 million deaths globally among children under age 5 years. The U5MR related to infections decreased by 70%, dropping from 1,022.3 per 100,000 in 1990 to 306.7 per 100,000 in 2021. The top three causes in 2021 were lower respiratory infections [76.3 per 100,000 (95% UI: 62.0 to 92.0)], malaria [64.5 per 100,000 (95% UI: 25.7 to 121.1)], and diarrheal diseases [51.7 per 100,000 (95% UI: 38.1 to 70.5)] (Table 1). Neonatal infection death cases accounted for 24.0% of the under-5 mortality from infections, with a comparatively moderate reduction rate of 58.7% over these 32 years, from 12,056.4 to 4,974.6 per 100,000. In neonates, the three most prevalent preventable infectious diseases were neonatal sepsis and other neonatal infections [2,118.5 per 100,000 (95% UI: 1,790.4 to 2,490.7)], lower respiratory infections [1,560.6 per 100,000 (95% UI: 1,308.9 to 1,835.7)], and non-HIV sexually transmitted infections [507.5 per 100,000 (95% UI: 187.6 to 1,030.9)]. Changes in the mortality burden of other infectious diseases are shown in Table S2.

The trends in infectious diseases showed inconsistent patterns across age groups. A significant decrease was observed in the global U5MR (EAPC −3.8%; 95% confidence interval (CI): −4.0% to −3.5%), while the hierarchical analysis exhibited a relatively smaller decline (EAPC −2.9%; 95% CI: −3.0% to −2.8%) in the overall neonatal mortality rate due to infections. The U5MR for routine vaccine-preventable diseases, including pertussis, diphtheria, tetanus, measles, tuberculosis, and hepatitis B, has decreased substantially from 196.0 per 100,000 in 1990 to 25.1 in 2021, with a more significant decline for measles among children aged 1–4 years (EAPC −8.1%; 95% CI: −8.7% to −7.5%]), and tetanus in neonates (EAPC −8.8%; 95% CI: −9.1% to −8.5%). However, a slight upward trend was noted in invasive non-typhoidal salmonella (EAPC 1.3%; 95% CI: 0.5% to 2.2%), dengue (EAPC 1.4%; 95% CI: 1.0% to 1.7%) and other neglected tropical diseases (EAPC 1.7%; 95% CI: 1.6% to 1.8%), especially among infants aged 6–11 months. The estimated annual reductions for the two leading causes of death among newborns—neonatal sepsis and other neonatal infections, and non-HIV sexually transmitted infections—were merely −0.9% (95% CI: −1.0% to −0.8%) and −1.4% (95% CI: −1.6% to −1.2%), respectively. Additionally, mortality rates of some infections exhibited phased trends, with HIV/AIDS being the most typical example in children aged 12–23 months. Prior to 2002, HIV/AIDS mortality rates rose gradually, but rapidly declined afterward, with an overall EAPC of −4.7% (95% CI: −6.5% to −2.9%). Ebola and Zika viruses experienced concentrated outbreaks in 2014 and 2016, respectively. For all infections, it appeared that the differences between males and females were small (Table S3).

Regional trends

The mortality rate for most infectious diseases decreased with rising SDI, whether in children under-5 age, infants or neonates (Table S4). Among the five SDI regions, the low SDI regions had the smallest percentage decline in the total mortality rate between 1990 and 2021 (Figures S1-S3). In high SDI regions, the percentage change (PC) of neonatal mortality rate for each infectious disease demonstrated a decline; while a marked escalation was observed in the U5MR of girls due to rabies (PC 65.4%; 95% UI: 18.6% to 110.1%). Meanwhile, the U5MR for HIV/AIDS showed the largest increases in middle SDI regions (male: PC 148.6%; 95% UI: 91.1% to 223.6%; female: PC 152.6%; 95% UI: 95.3% to 224.1%), followed by high-middle SDI regions (male: PC 32.1%; 95% UI: 16.9% to 61.2%; female: PC 60.2%; 95% UI: 43.0% to 92.2%).

The composition of infectious disease burdens also changed across the 21 geographical regions over 32 years (Figure 1). In Sub-Saharan Africa, the proportion of DALYs attributed to measles declined obviously among infants and children under 5 years of age, while malaria increased. In high-income regions, the proportion of DALYs for upper respiratory infections in 2021 was 1.5 to 3.0 times that of 1990, whereas the proportion for lower respiratory tract infections was one-third to one-half of what it was in 1990. As for neonates, the burdens of lower respiratory infections, diarrhea, and tetanus decreased; however, the proportions of neonatal sepsis and non-HIV sexually transmitted infections nearly doubled, or even more, in certain regions—such as Latin America, East Asia, North Africa, and the Middle East—in 2021 compared to 1990 (Figures S4,S5).

Figure 1 Proportions of each infectious disease burden among children under 5 years of age by regions between 1990 and 2021. Each colored area represents the proportion of deaths (A) or DALYs (B) from a specific infectious disease relative to the total number of deaths or DALYs caused by infections in that year. AIDS, acquired immunodeficiency syndrome; DALYs, disability-adjusted life-years; HIV, human immunodeficiency virus.

In terms of temporal trend in regions, the overall mortality rate of infectious diseases in East Asia decreased most significantly during the study period, whether among children under 5 years of age, infants, or neonates (Figure 2, Table S5). The U5MR for routine vaccine-preventable diseases demonstrated more pronounced downward trends in Latin America regions, with the maximum EAPC of −36.6% (95% CI: −41.2% to −31.6%) for measles, −15.5% (95% CI: −16.0% to −15.1%) for tetanus, −15.1% (95% CI: −20.2% to −9.6%) for diphtheria, and −25.8% (95% CI: −28.8% to −22.7%) for rabies. The annual estimated mortality rates for HIV/AIDS in South Asia, East Asia, and Oceania rose by 6.4% (95% CI: 2.5% to 10.5%), 7.7% (95% CI: 6.4% to 9.1%), and 8.9% (95% CI: 5.0% to 12.9%), respectively; similarly, there was an increase in North Africa and Middle East (EAPC 3.9%; 95% CI: 2.8% to 5.0%), and Eastern Europe (EAPC 3.3%; 95% CI: 2.6% to 4.0%). Regarding tropical infections, mortality due to dengue showed an upward trend in North America (EAPC 8.4%; 95% CI: 7.2% to 9.5%), Australasia (EAPC 11.5%; 95% CI: 9.2% to 13.7%), Tropical Latin America (EAPC 6.2%; 95% CI: 4.5% to 8.0%), and Central Sub-Saharan Africa (EAPC 6.8%; 95% CI: 5.5% to 8.1%); so did rabies in North America (EAPC 2.7%; 95% CI: 2.0% to 3.3%), Western Europe (EAPC 3.4%; 95% CI: 2.2% to 4.5%), Australasia (EAPC 6.4%; 95% CI: 1.6% to 11.3%) and Oceania (EAPC 3.4%; 95% CI: 2.6% to 4.2%). Mortality attributable to malaria declined more substantially in Central Asia (EAPC −31.8%; 95% CI: −39.6% to −23.0%) and East Asia (EAPC −25.7%; 95% CI: −27.6% to −23.7%), whereas not pronounced or even slightly increased in Southern Sub-Saharan Africa (EAPC 1.9%; 95% CI: 0.7% to 3.2%). Mortality due to leishmaniasis increased substantially in Western Sub-Saharan Africa (EAPC 7.4%; 95% CI: 3.9% to 11.1%).

Figure 2 Region-level heatmap for mortality EAPC due to each infectious disease among children under 5 years of age between 1990 and 2021. The shading of EAPC for mortality rates of infectious diseases ranges from dark blue, indicating a rapid decline, to dark red, signifying a rapid increase. The number in each cell represents the value of EAPC. AIDS, acquired immunodeficiency syndrome; EAPC, estimated annual percentage change; HIV, human immunodeficiency virus.

National trends

The mortality rates for infectious diseases overall varied widely across countries (Figure 3). In 2021, South Sudan had the highest infection-related mortality rates among children under 5 years of age [1,562.6 per 100,000 (95% CI: 1,543.2 to 1,582.2)] and neonates [16,058.8 per 100,000 (95% CI: 15,634.8 to 16,489.7)]. Conversely, Norway had the lowest death rate for children under 5 years of age, at 2.1 per 100,000 (95% CI: 0.8 to 4.7), while Japan recorded the lowest rate for neonates, at 61.0 per 100,000 (95% CI: 43.6 to 83.1). In addition, significant inter-country discrepancies existed in U5MR trends from 1990 to 2021. China experienced the most substantial decline in U5MR due to infectious diseases with an EAPC of −9.8% (95% CI: −10.1% to −9.5%). The slightest decrease was observed in Brunei Darussalam (EAPC −0.9%; 95% CI: −1.2% to −0.6%). With respect to the neonatal mortality rate, the largest decline was seen in Kyrgyzstan (EAPC −8.4%; 95% CI: −8.9% to −7.9%), while small increases were observed in Dominica (EAPC 1.7%; 95% CI: 1.1% to 2.3%) and Guam (EAPC 1.1%; 95% CI: 0.6% to 1.7%). More detailed information is presented in Tables S6,S7.

Figure 3 Under-5 mortality rates, percentage changes and EAPC for overall infectious diseases at national level between 1990 and 2021. (A) Under-5 mortality rates for infectious diseases overall in 2021. (B) Percentage changes of under-5 mortality rates for infectious diseases overall from 1990 to 2021. (C) EAPC of under-5 mortality rates for infectious diseases overall between 1990 and 2021. EAPC, estimated annual percentage change.

Forecasts

Globally, over the past 32 years, there has been a relatively larger decline in the disease burden contributed by respiratory infections and tuberculosis (59.1%) and enteric infections (62.8%); which the declines were comparatively smaller for HIV/AIDS and sexually transmitted infections (19.3%), neglected tropical diseases and malaria (13.0%), as well as neonatal sepsis and other neonatal infections (15.8%). At the regional level, the variations in infectious disease burden were primarily concentrated on the latter three categories of infections. For instance, in the Central Europe, Eastern Europe, and Central Asia regions, the burden of neonatal sepsis and other neonatal infections saw the smallest decline (4.9%), with HIV/AIDS and sexually transmitted infections even increasing (7.7%). However, both infections showed significant declines in high-income regions, with reductions of 36.7% and 53.1%, respectively (Figure 4, Table S8).

Figure 4 Change in disease burden contributed by specific infectious diseases among children under 5 years of age, by super-regions, from 1990 to 2021 and 2021 to 2030. (A) Change in disease burden due to infectious diseases from 1990 to 2021. (B) The projected change in disease burden due to infectious diseases from 2021 to 2030. Each color represents a category of infectious diseases. The percentage values represent the proportion of increased or decreased deaths due to changes in the risk exposure levels of specific infections from 1990 to 2021 (or from 2021 to 2030), relative to the total number of deaths caused by that infection in both 1990 and 2021 (or 2021 and 2030). A negative value indicates that the burden of infection has increased in 2021 (or 2030) compared to 1990 (or 2021) in the absence of effective control measures. In contrast, a positive value signifies the successful implementation of interventions that have effectively reduced mortality rates. See Supplementary Methods for details. AIDS, acquired immunodeficiency syndrome; HIV, human immunodeficiency virus.

By 2050, the overall global mortality rate of infectious diseases among children under-5 age was projected to decrease to approximately 174.5 per 100,000 (Figure 5). However, the burden due to HIV/AIDS and sexually transmitted infections, will probably rise in three regions, South Asia (6.7%), Latin America and Caribbean (9.1%), and Southeast Asia, East Asia, and Oceania (5.4%) by 2030. Of note, the mortality rates of HIV/AIDS and sexually transmitted infections in South Asia were projected to increase significantly after 2040, reaching 960.1 per 100,000 by 2050. Respiratory infections and tuberculosis mortality in most regions were projected to experience a transient surge around 2022, followed by a rapid decline (Figures S6-S11).

Figure 5 Forecasts of total mortality rates attributable to infectious diseases among children under 5 years of age, by super-regions between 2022 and 2050. Bayesian Age-Period-Cohort model is used to forecast the future trends. In these stacked bar charts, each color represents the predicted mean values of corresponding disease. AIDS, acquired immunodeficiency syndrome; HIV, human immunodeficiency virus.

Discussion

This study provides, for the first time, trends in overall and specific infectious disease burdens among children under 5 years of age worldwide between 1990 and 2021. We confirmed a significant downward trend in overall mortality rates due to infections, with a particularly notable decrease in vaccine-preventable diseases. Nonetheless, the burden of tropical diseases and HIV/AIDS remained substantial, and in certain regions, including high-income areas, there was a concerning upward trend. Neonatal mortality due to infections still posed a considerable threat. Enhancing infection prevention and control during the antenatal and neonatal periods is the top priority for further reducing the U5MR.

One of the primary factors contributing to the decline in childhood infectious mortality rates is the growing ubiquity of vaccination programs. Our data showed that the global U5MR for routine vaccine-preventable diseases demonstrated a substantial decline of 87.2% between 1990 and 2021. This highlights the significance of childhood vaccination as a paramount preventive strategy that saves substantial healthcare costs and lives and mitigates productivity losses (19,20). In the context of the widespread immunization efforts that have contributed to a significant reduction in global childhood pneumonia mortality, our projections indicate a temporary increase in rates around 2022, potentially attributable to the impact of the coronavirus disease 2019 (COVID-19) pandemic.

Another significant finding is that tropical diseases and HIV/AIDS have become new crises in pediatric infections that cannot be ignored, even in regions with high or high-middle SDI. The vectors may migrate by population movements, travels, and trades, which may contribute to the resurgence of tropical diseases in high-income regions (21,22). Some neglected infections, including dengue, which were once thought to be eradicated, have not received the same level of attention as other infectious diseases, resulting in a limited prevention and treatment experiences in those areas. More worrisomely, childhood tropical disease burdens nowadays appear on the rise, yet fewer trainees opt to specialize in this field (23,24). HIV/AIDS is another concern in infectious diseases, with its impact not confined to Sub-Saharan Africa and South Asia. Alarmingly, the HIV/AIDS crisis among children under 5 years of age is escalating in Eastern Europe, North Africa and Middle East, Asia, and Oceania. This may be more closely related to social instability/vulnerability, where regional conflicts can destabilize social order, reduce HIV/AIDS perinatal prevention services, destroy healthcare infrastructure, and exacerbate drug epidemics, ultimately leading to increases in mother-to-child transmission of HIV/AIDS (25). Our forecasts indicated a sharp increase in HIV/AIDS among children in South Asia after 2040, further highlighting the critical need for enhanced HIV/AIDS prevention regional strategies.

For neonatal mortality, it did not show a meaningful decline during the study years. The proportional contributions to under-5 mortality of the two major neonatal infections—neonatal sepsis and non-HIV sexually transmitted infections—increased compared to other infectious diseases by 2021. Although the prevention and treatment of neonatal sepsis is recognized as one of the essential interventions for reproductive, maternal, newborn and child health by World Health Organization (26-28), the progress in implementing this policy for all newborns across countries remains uneven due to disparities in socioeconomic development. Crafting individualized strategies tailored to the specific conditions of each nation is crucial to addressing the issue. As for sexually transmitted infections, routine screening for chlamydial, gonorrheal, and trichomonal infections to prevent adverse pregnancy and newborn outcomes is recommended only in a few countries (29,30), limiting the prompt therapy for pregnant women with these infections.

The inequality in mortality between countries has become increasingly pronounced, which may be influenced by socioeconomic development status, social stability, health care and public health infrastructures (31,32). In the present study, the number of infection-related under-5 mortality in Sub-Saharan Africa accounted for 69% of worldwide total in 2021. However, this situation is not irreversible. We found that several countries with middle- and low-middle SDI demonstrated remarkable progress in lowering the mortality rate of children under 5 years of age, infants and neonates, with the most pronounced decline in China. This success achieved can be largely credited to a comprehensive suite of government public health policies, such as the Plans of an Expanded National Immunization Programme (2008), and the National Development Plan for Children in Poor Areas (2014–2020), which may provide valuable lessons for countries facing similar resource constraints (33,34). Furthermore, we also find that Brazil has made significant progress in reducing infant and child mortality through key initiatives within its Unified Health System, including family planning, prenatal care, childbirth assistance, breastfeeding guidance, neonatal consultations, and child health monitoring (35). And Turkey’s launch of the Health Transformation Program in 2003 to achieve universal health insurance contributed significantly to the decline in child mortality (36).

Our study has limitations. First, the GBD data is predicated on the assumption that each death can be attributed to a single underlying cause. Nonetheless, in reality, there is often a complex interplay of multiple causes, which limits the ability to analyze cases with multiple infections (2). Second, the accuracy of trend estimations for the burdens of infectious diseases is contingent upon the quality and integrity of the original data. For a few countries with low incomes or those affected by war and natural disasters, it may be difficult to ensure the completeness of the original data, affecting the accuracy of trend assessments in these nations. Third, infectious diseases selected in this study are preventable ones mentioned in Sustainable Development Goal 3.2 (4). Rare infectious diseases are not included, which might have a negligible impact on the observed mortality due to infections overall. Fourth, due to the unavailability of regional raw datasets, we used CIs rather than UIs to evaluate the summed rate of infectious diseases, which means we cannot comprehensively reflect the multi-source errors of real-world complex systems. Empirical validation studies are needed to assess the epidemiological validity of these estimates. Lastly, the time frame from 2021 to 2050 is vulnerable to some uncontrollable or unknown factors in the future, which may have certain influence on the projected trends.

Conclusions

The global burden of infectious diseases among young children remained a significant public health concern, even though it declined steadily in the last 32 years. More attention is warranted to neglected tropical diseases, HIV/AIDS, and neonatal infections. The resurgence of some infectious diseases in middle- and high-income regions warrants elevated vigilance. Regional disparities in U5MR underscore the necessity for targeted prevention and care strategies in maternal and child health tailored to specific burdens and trends, thereby accelerating the achievement of Sustainable Development Goal 3.2 across all regions.

Acknowledgments

We are deeply grateful to the Institute for Health Metrics and Evaluation staff and its GBD collaborators for their invaluable contributions in providing the data that underpinned this study.

Footnote

Reporting Checklist: The authors have completed the GATHER reporting checklist. Available at https://tp.amegroups.com/article/view/10.21037/tp-2026-1-0064/rc

Peer Review File: Available at https://tp.amegroups.com/article/view/10.21037/tp-2026-1-0064/prf

Funding: This study was supported by the National Key Research and Development Program of China (No. 2022YFC2705300).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-2026-1-0064/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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