This analysis offers a comprehensive assessment of the global burden of viral LRTDs from 2010 to 2021, underscoring both the relative stability and the dramatic shifts that have occurred over the past decade. Between 2010 and 2019, viral LRTD episode rates remained relatively consistent, primarily driven by common pathogens like influenza and RSV. However, hospitalisation rates for viral LRTD increased by 40% during this period, suggesting increasing severity of illness, possibly due to factors such as changes in healthcare access, improvements in diagnostic capabilities, shifts in viral virulence, or increasing prevalence of comorbid conditions, which may negatively impact clinical outcomes. The emergence of SARS-CoV-2 in 2020 brought about a profound transformation in the epidemiology of viral LRTD. In 2020 and 2021, episode and hospitalisation rates surged by orders of magnitude due to the pandemic, with COVID-19 causing a substantial increase in both clinical severity and healthcare demand.

Importantly, this study provides the first internally consistent, globally comprehensive assessment tracking five distinct viral aetiologies and three severe clinical endpoints (i.e., ICU need, IMV need, in-hospital deaths) simultaneously across 204 countries over a 12-year window. Before this analysis, pathogen-specific global estimates tracking shifting clinical severity over time were severely limited. This unified framework enables the quantification of these essential estimates for structural health system planning and resource allocation, which can be iteratively updated as additional data become available.

Geographically, the burden of viral LRTD was not evenly distributed. In the years leading up to the pandemic, regions like South Asia had the highest rates of viral LRTD episodes, while North America had the highest hospitalisation rates, likely influenced by healthcare infrastructure and reporting standards [10, 11]. The pandemic, however, caused significant shifts in these patterns. Eastern Europe including Russia, for instance, saw some of the greatest increases in both episode and hospitalisation rates during 2020–2021, outcomes likely due to weaker healthcare systems and delayed vaccination campaigns that were notably exacerbated by widespread misinformation and disinformation regarding COVID-19 vaccines across the region [12]. In contrast, regions like East Asia and Australasia showed more contained surges, attributable to earlier and more stringent public-health responses [13, 14]. The comparatively muted rise in documented hospitalisations across many low- and middle-income countries in other regions likely reflects barriers to care access and diagnostic capacity constraints rather than lower disease burden. These findings highlight the crucial role of timely, evidence-informed public-health responses and healthcare system preparedness in mitigating the impact of viral LRTD outbreaks. Estimates of viral LRTD hospitalisations and clinical outcomes in our analysis were generally lower (often two to three times lower) than those reported in other studies, likely reflecting differences in study design, including geographical coverage and case definitions (e.g., GBD LRTD versus broader respiratory infectious disease categories) [15,16,17].

The demographic patterns observed in this study further reinforce the critical need to protect vulnerable populations. Older adults (≥ 65 years) were the most consistently affected group across all clinical outcomes, experiencing significantly higher rates of hospitalisations, ICU need, and in-hospital mortality. This demographic remains highly vulnerable to severe outcomes from viral respiratory infections, primarily due to age-related immune senescence and the high prevalence of comorbidities in this group [18, 19]. As health systems worldwide face increasing pressure from ageing populations and rising emergency-care demand, strengthening prevention and treatment strategies for respiratory infections in older adults will be essential to mitigate future strain. The high incidence of IMV need among neonates further brings attention to the heavy clinical burden on the youngest age groups, which warrants further research and public health interventions. These findings also point to the importance of age-specific strategies, including vaccination and early detection, as part of a comprehensive approach to reducing morbidity and mortality from viral LRTD. In this context, vaccine hesitancy—particularly among older adults—may limit coverage and reduce the potential population-wide impact of vaccination, further contributing to the observed burden [20].

While the ageing global population likely contributed to the overall increase in severe clinical outcomes over the past decade, the COVID-19 pandemic accelerated these trends dramatically. By 2021, SARS-CoV-2 was responsible for more than double the ICU need rates and more than triple the mortality compared to pre-pandemic levels. The observed rise in severity is likely multifactorial, with factors such as the emergence of more virulent variants of the virus and shifts in clinical practice (e.g., lower thresholds for ICU need) all playing significant roles [21, 22]. In addition, the limited availability of effective therapeutic options for hospitalised and severely ill patients—particularly during the early phases of the pandemic—likely contributed to poorer clinical outcomes, pointing to persistent gaps in treatment strategies for severe viral LRTDs. The variable availability of vaccines across regions also compounded these disparities, further exacerbating the global burden [23]. Collectively, these findings reinforce the necessity of equitable vaccine distribution alongside continued innovation in therapeutics and preparedness for future viral LRTD outbreaks, including both vaccine development and strategies for rapid deployment in diverse global settings.

An important consequence of the COVID-19 pandemic was the redistribution of the global viral LRTD burden. During the peak years of the pandemic, viral LRTD episodes and hospitalisations attributed to other pathogens, including influenza, RSV, and hMPV, decreased by nearly 50%. This redistribution likely reflects the success of public health measures designed to control the spread of SARS-CoV-2, such as travel restrictions, social distancing, and increased hygiene practices, which simultaneously reduced the transmission of other respiratory viruses [24, 25]. The reduction in the burden of other viral pathogens emphasises the dynamic nature of viral epidemiology and suggests that interventions for one pathogen can have widespread effects on the transmission of others. As these patterns continue to evolve, evaluating post-pandemic trends will be critical to understanding the re-emergence of pathogens, potential changes in virulence, and shifting patterns of population susceptibility. This demonstrates the need for a broader, more integrated approach to viral surveillance, one that considers the interactions between multiple respiratory pathogens and the full range of public health measures. These findings also establish a critical benchmark, essential for understanding post-pandemic re-emergence patterns, shifts in population susceptibility, and evolving aetiology-specific dynamics.

Our estimates which demonstrate marked regional variations in viral LRTD burden may reflect the complex interplay of epidemiological, structural, and economic factors. While the HAQ Index and SDI were significant predictive covariates in our models quantifying population-level unmet need for preventive and therapeutic interventions, we cannot identify whether this unmet need stems from a lack of therapeutic interventions, access barriers, or staffing constraints. In high-income countries, existing healthcare infrastructure may have facilitated the management of surges in cases, including the provision of intensive care and mechanical ventilation. By contrast, in low- and middle-income countries, more limited healthcare resources and infrastructure, including delays in vaccine distribution, could have contributed to heightened vulnerability during the pandemic [26, 27]. These patterns may also reflect differences in access to diagnostic tools, vaccines, and therapeutic interventions [23]. Together, these observations stress the importance of strengthening healthcare systems globally, with particular attention to intensive care capacity, robust viral surveillance, and equitable access to healthcare resources [23, 27]. They also underline the need to prioritise global health equity to ensure that all populations, particularly those in resource-constrained settings, can access preventive and therapeutic measures to mitigate the burden of viral LRTDs.

The rapid changes in viral LRTD epidemiology brought about by the COVID-19 pandemic also emphasise the importance of timely and accurate data collection. Surveillance systems must be able to quickly capture and track emerging trends in viral infections, allowing for a swift public health response. Global health systems must be better equipped to handle the complexity of tracking multiple pathogens simultaneously, as the pandemic has shown how interwoven global viral dynamics can be [28]. This requires a holistic approach to surveillance, one that includes data on aetiology-specific viral infections, clinical outcomes, and healthcare infrastructure capacity, among other factors. Real-time surveillance data would enable more precise forecasting and resource allocation, ensuring that public health responses are appropriately tailored to meet the demands of an outbreak. Clear and timely communication of public health threats is also critical to ensure that surveillance findings translate into effective action, with targeted public health messaging and sustained community education helping to mitigate the impact of misinformation during outbreaks. In addition to strengthening surveillance, there is an urgent need to enhance in-hospital management strategies and intensive care capacity, as rising trends in ICU and IMV needs may exceed the limits of existing healthcare systems. At the same time, improved prevention and management of chronic conditions associated with severe LRTD outcomes may reduce the size of vulnerable populations during future outbreaks, complementing investments in acute care capacity Addressing these challenges will require investment in workforce training and medical education, expansion in intensive care resources, and the development of context-appropriate clinical guidelines to ensure that healthcare systems are resilient and able to adapt to future surges of severe LRTD cases.

This analysis has several limitations. First, bronchitis cases without diagnoses of bronchiolitis or pneumonia are not captured in our estimates of LRTD estimates, as bronchitis alone does not meet the GBD LRTD case definition, potentially leading to underestimation of viral LRTD burden. Some studies suggest that bronchitis represents a relatively modest proportion of lower respiratory infection admissions and the magnitudes differ across age groups and healthcare settings, with estimates ranging from ~ 6% to 15% in observed cohorts, and thus is unlikely to substantially alter overall burden patterns [29]. We were also unable to assess the timing of infection in relation to hospital admission or severity, as these details were not consistently available in the underlying data. Additionally, hospitalisation scalars, although adjusted by HAQ Index for location-specific access, were derived from three high-income settings (e.g., USA, Poland, and Taiwan) and may not fully reflect care-seeking behaviours in low-resource settings.

Data limitations were particularly pronounced in low-income settings, where the burden of viral LRTD may be highest. DisMod-MR 2.1 estimates are contingent on the quality and representativeness of input data; in these locations, modelled estimates relied heavily on covariates such as the HAQ Index and SDI, as well as data from similar geographies, resulting in less precise estimates with wider UIs. While necessary, this modelling approach may lead to under- or overestimation of burden depending on covariate relationships and comparability of diagnostic practices. Differences in test performance and population testing strategies may also introduce bias in the attribution of specific viral aetiologies. Specifically, granular diagnostic practices such as multiplex PCR testing and bronchoscopic sampling are unevenly distributed across clinical settings and geographies, leading to potential underestimation of viral aetiologies. This diagnostic underestimation is likely disproportionately present in low- and middle-income countries, as well as resource-constrained settings with high-income countries where access to advanced molecular testing platforms is limited. The limited availability of post-pandemic data further adds uncertainty, constraining the precision of current burden estimates and future modelling.

Although our methodology aims to harmonise data across sources, some heterogeneity remains. Variability in case definitions (e.g., “medically attended” versus “clinician-diagnosed”) and national reporting requirements may contribute to aetiology-specific or regional biases. We were also unable to analyse more granular viral subtypes, such as influenza A versus B, due to data constraints.

Finally, the use of annual data limited our ability to assess seasonal or short-term trends. Co-infections were counted in multiple aetiology categories, which may have influenced pathogen-specific estimates. In addition, limited testing for less common viruses may have contributed to an underestimation of the burden of LRTD due to “other” viruses. Estimates of ICU and IMV needs were extrapolated from data-rich settings using age-specific ratios, assuming that these ratios are constant across settings and that observed utilisation accurately reflects underlying clinical need. Clinical outcomes by aetiology were stratified by age, but not by sex or year, due to data sparsity.

This study has several key strengths. First, it represents the first internally consistent, globally comprehensive assessment of viral LRTD episodes, hospitalisations, and clinical outcomes, including COVID-19, across 233 locations and regions, 26 age groups modelled in the GBD, and multiple demographic subgroups. By leveraging well-established GBD methods, this analysis provides internally consistent and comparable estimates of viral LRTD burden, even in regions with limited data availability.

Another strength of this study is the inclusion of ICU needs, modelled based on healthcare utilisation patterns from data-rich regions. This allows for a global estimation of unmet needs for intensive care services, including mechanical ventilation, regardless of local healthcare infrastructure. The study’s comprehensive approach, encompassing a range of viral aetiologies, both prior to and during the COVID-19 pandemic, offers valuable insights into the impact of the pandemic on global health systems and the need for continued investment in healthcare capacity and viral surveillance. Furthermore, our approach establishes a modelling framework that can be iteratively updated as additional data become available in the future, ensuring access to up-to-date estimates of the burden of viral LRTD to inform global health policy and clinical practice.