PMID: 40082958 https://pubmed.ncbi.nlm.nih.gov/40082958/

Abstract

BACKGROUND: Current evidence on influenza vaccine effectiveness (VE), which is predominately derived from small high-risk older populations and focuses on specific influenza-related complications, might not be generalizable to real-world older populations with diverse characteristics in Taiwan. Therefore, this observational study with a target trial emulation framework aimed to evaluate the clinical effectiveness of an influenza vaccine on influenza infection, complications, and associated healthcare utilization and costs.

METHODS: 1,214,392 propensity-score-matched pairs of vaccinated and unvaccinated older populations from the influenza season of 2018/2019 were identified from Taiwan's National Health Insurance Research Database. VE (estimated as 1 minus hazard ratio [HR]*100%) and the HRs were used for influenza events and associated complications, respectively.

RESULTS: Primary analyses show 14% (10-18%) of VE against influenza-associated hospitalization, irrespective of age, frailty status, and underlying influenza risk. Notably, a decline in VE for influenza-associated hospitalization was observed when the observational period following vaccination was extended (25% [19-30%], 23% [18-28%], and 14% [10-18%] for the intervals October 2018-March 2019, October 2018-May 2019, and October 2018-September 2019, respectively). Compared with non-vaccination, having an influenza vaccination significantly reduced risks of influenza-associated death by 30%, various respiratory by 12-26%, cardiovascular complications by 39-47%, and acute kidney injury by 23%. Approximately savings of USD 3,000,000 in total from averting influenza-associated hospitalization following vaccination were found. The non-significant effects of the influenza vaccine on negative control outcomes support the validity of the study procedures.

CONCLUSIONS: VE for severe influenza events (i.e., those requiring hospitalization) and related complications among the real-world older population was corroborated. To avoid severe influenza episodes and complications and minimize associated economic consequences, continuous influenza vaccine uptake over different influenza seasons is recommended for this population.