Trends in Influenza-Associated Lower Respiratory Tract Infection Burden and Influenza Vaccination Coverage among Adults Aged >=55 Years in China, 1990-2023

ABSTRACT Background Influenza-associated lower respiratory tract infections (LRTI) impose substantial disease burden on older populations globally. While China has experienced rapid aging, comprehensive assessment of long-term trends in influenza-associated LRTI burden and vaccination coverage among adults aged [≥]55 years remains limited. Methods We extracted age-standardized mortality and disability-adjusted life years (DALYs) rates of influenza-associated LRTI among Chinese adults aged [≥]55 years from the Global Burden of Disease Study 2023 (GBD 2023). Estimated annual percentage change (EAPC) and age-period-cohort (APC) models were employed to analyze long-term trends (1990-2023). Using the China Health and Retirement Longitudinal Study 2020 (CHARLS 2020, n=13,815), we performed multivariable logistic regression to identify factors associated with influenza vaccination uptake. Spearman correlation assessed ecological associations between GBD age-specific mortality rates and CHARLS vaccination coverage across nine age groups. Results Age-standardized mortality rates declined from 4.09 to 0.31 per 100,000 (EAPC=-8.02%, 95%CI: -9.08% to -6.95%), and DALYs rates from 177.63 to 6.06 per 100,000 (EAPC=-10.67%), representing >96% reductions from 1990 to 2023. Deaths dropped sharply by 59.6% in 2020, consistent with protective effects of non-pharmaceutical interventions during COVID-19. The [≥]85-year age group showed the slowest improvement (EAPC=-5.63%). Influenza vaccination coverage in CHARLS 2020 was only 15.1%. Older age ([≥]85 years: OR=0.65, 95%CI: 0.46-0.92) and higher educational attainment (college or above: OR=0.34, 95%CI: 0.20-0.56) were independently associated with lower vaccination rates, though the small sample size in the highest education group (n=68) warrants cautious interpretation. Ecological analysis revealed a significant negative correlation between GBD mortality rates and CHARLS vaccination coverage (r=-0.700, p=0.036, n=9 age groups), indicating a "protection mismatch" phenomenon. Raising vaccination coverage to 75% (WHO target) could prevent approximately 2,041 deaths annually under moderate vaccine efficacy assumptions, with [≥]75-year-olds contributing 82.7% of preventable deaths. Conclusions Influenza-associated LRTI burden has declined substantially among Chinese adults aged [≥]55 years, but improvement is slowest in the oldest age groups. Vaccination coverage remains critically insufficient with a persistent "protection mismatch" where those at highest mortality risk have lowest coverage. Adults aged [≥]75 years face a "triple vulnerability" of high mortality, low vaccination coverage, and high COPD comorbidity prevalence, and should be prioritized for vaccination to maximize preventable mortality benefits.