Global Viral Lower Respiratory Disease Episodes, Hospitalisations, and Clinical Outcomes by Aetiology, 2010-2021

Viral lower respiratory tract disease (LRTD) is a major cause of global morbidity and mortality, but pathogen-specific estimates remain limited. We aimed to quantify the global burden of viral LRTD episodes, hospitalisations, and severe clinical outcomes by aetiology from 2010 to 2021.

We used the Global Burden of Disease (GBD) 2021 modelling framework to generate estimates of viral LRTD incidence, hospitalisations, and clinical outcomes from 2010 to 2021 for 204 countries and territories, 21 regions, and seven super-regions. Aetiology-specific estimates were generated for five viral categories: influenza, respiratory syncytial virus (RSV), human metapneumovirus (hMPV), SARS-CoV-2, and "other" viral pathogens. Data inputs included surveillance systems, clinical informatics, published literature, surveys, and vital registration. Viral LRTD incidence was estimated using DisMod-MR 2.1, a GBD Bayesian meta-regression tool for disease incidence. We then applied location-specific admission scalars, adjusted for healthcare access, to derive hospitalisations. Aetiology-specific clinical outcome proportions-including intensive care unit (ICU) need, invasive mechanical ventilation (IMV) need, and in-hospital mortality-were estimated using meta-regression-Bayesian, regularised, trimming models. These were then applied to the hospitalisation estimates. COVID-19 incidence and hospitalisations were estimated using established GBD COVID-19 methods. All estimates are reported with 95% uncertainty intervals (UIs).

Globally, viral LRTD episodes increased from 82.3 million (95% UI 76.4-88.2) in 2010 to 94.9 million (88.8-101.2) in 2019, while episode rates remained relatively stable at approximately 1200 per 100,000 population. Over the same period, hospitalisation rates increased by 40%, from 103.7 (96.1-111.4) to 145.4 (134.6-156.4) per 100,000 population. In 2020 and 2021, the emergence of SARS-CoV-2 resulted in sharp increases in burden, with episodes exceeding 1.1 billion in 2020 and 1.5 billion in 2021. During this period, 2020-2021, episode and hospitalisation rates associated with influenza, RSV, and hMPV declined by nearly 50%. Between 2010 and 2019, global rates of ICU need increased from 16.1 (14.3-18.0) to 23.7 (21.0-26.6) per 100,000 population, IMV need from 7.5 (6.7-8.4) to 11.2 (10.0-12.6), and in-hospital mortality from 9.4 (8.4-10.5) to 13.9 (12.3-15.6). In 2020-2021, SARS-CoV-2 dominated severe outcomes, with in-hospital mortality reaching 87.7 (83.3-92.2) per 100,000 population in 2021. Across the study period, older adults consistently experienced the highest rates of severe outcomes, and substantial regional variation was observed.

Before 2020, global incidence of viral LRTD was stable; however, hospitalisations and severe outcomes increased substantially, suggesting rising clinical severity and healthcare demand. The COVID-19 pandemic profoundly altered the global viral LRTD landscape, driving unprecedented increases in hospitalisations, intensive care use, and mortality, while suppressing other respiratory viruses in the years 2020 and 2021. These findings demonstrate a substantial burden of severe viral LRTD globally, with marked age and regional variations, underscoring the importance of sustained aetiology-specific surveillance, adequate healthcare capacity, and equitable access to preventive and therapeutic interventions.