Global burden of influenza lower respiratory tract infections in children younger than 5 years from 1990 to 2021.

Background: Influenza lower respiratory tract infections (LRTIs) impose substantial mortality burden in children under five globally, yet, comprehensive analyses of their long-term spatiotemporal disease burden patterns remain underexplored. The research aimed to estimate the death and disability-adjusted life years (DALYs) caused by influenza LRTIs for children under five in 204 countries and territories over the period 1990 to 2021. Methods: Epidemiologic data on influenza LRTIs, including death and DALYs, were extracted from the Global Burden of Disease (GBD) 2021 database across global, regional, and national strata. Results: Globally, influenza LRTIs caused 27,615 [95% uncertainty interval (UI): 20,128-36,852] deaths and 2,460,833 (95% UI: 1,796,287-3,280,725) DALYs in children under five in 2021, representing an 83.46% decline in deaths and 83.47% reduction in DALYs since 1990. Death and DALY rates decreased by 84.41% and 84.43%, respectively, with accelerated declines after 2020. Boys consistently exhibited higher mortality and DALYs across, with the largest gender disparity in neonates aged 0-6 days. The 1-5 months age group remained the most vulnerable, though all age strata showed marked burden reductions compared to 1990. Low socio-demographic index (SDI) regions bore the highest burden in 2021, with death and DALY rates of 9.42 and 837.39 per 100,000, despite experiencing the most substantial percentage reductions. Consistent with this pattern, the socioeconomic inequality analysis revealed a substantial narrowing of absolute disparities [slope index of inequality (SII): -4,703.6 to -581.9] concurrent with a deepening of relative inequality [concentration index (CI): -0.46 to -0.61]. Western Sub-Saharan Africa and South Asia had the highest absolute mortality (10,145 and 9,382 deaths) and DALYs (900,693 and 839,480). Conclusions: From 1990 to 2021, the global burden of influenza LRTIs in children under five showed a significant decline, with accelerated progress during the coronavirus disease 2019 (COVID-19) pandemic. However, low SDI regions exhibited the steepest declines yet retained the highest mortality rates, with the burden becoming increasingly concentrated in these areas. These findings highlight the urgent need for equitable vaccine distribution, strengthened neonatal care in high-burden areas, and gender-sensitive health policies to achieve Sustainable Development Goal 3.2 and mitigate preventable child deaths.