A comparative study of incidence rate and severity of influenza virus and respiratory syncytial virus associated hospitalisation in older adults in Jiangsu Province, China: a retrospective analysis of a regional medical database.

Background: Few studies have compared the disease burden between influenza virus (IFV) and respiratory syncytial virus (RSV) in older adults, particularly outside high-income countries. We aimed to compare IFV- and RSV-associated hospitalisation burden and severity in older adults in Jiangsu Province, China. Methods: Drawing on a medical database from Jiangsu Province, an economically-developed province in eastern China, we included acute respiratory infections (ARI) admission records in adults aged ≥60 years during 2020 to 2023, linked with viral testing data, where available. We applied a time-series regression model for estimating RSV- and IFV-associated hospitalisation rates by year, age group, and sex. We compared disease severity, defined as a composite of mechanical ventilation use, intensive care unit (ICU) admission, or in-hospital mortality, between RSV- and IFV-positive cases using multivariable logistic regression, with adjustments for age, sex, year, region, and laboratory method. Results: We included 188 529 ARI hospitalisation episodes during the study period. RSV and IFV had comparable hospitalisation rates, peaking in 2023 at 98 per 100 000 person-years (95% confidence interval (CI) = 81-115) for RSV and 116 per 100 000 person-years (95 CI = 100-133) for IFV. Hospitalisation rates increased with older age and were marginally higher in males. The risk for severe cases was 1.47 (95% CI = 1.086-1.997, P = 0.013) times higher in RSV than in IFV. Older age and being males were independent risk factors for severe cases. Conclusions: We found the RSV hospitalisation burden to be comparable to that of IFV in older adults, albeit with higher severity. The findings contribute to the evidence base for recommendation of RSV and IFV vaccination in older adults in China.