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Updated: Sep 8, 2025
An Optimized Hemagglutination Inhibition HI Assay to Quantify Influenza-specific Antibody Titers
Published on: December 1, 2017
Assessment of influenza vaccine effectiveness among the elderly in Taiwan using population-based registry data for
Yi-Ting Huang1, Tsung-Pei Tsou2, Szu-Han Kuo2
1Institute of Statistical Science, Academia Sinica. No.128, Academia Road, Section 2, Nankang, Taipei 11529, Taiwan; Institute of Epidemiology and Preventive Medicine, National Taiwan University, Room 501, No.17, Xu-Zhou Road, Taipei 100, Taiwan.
Introduction:
Influenza infection can cause serious complications in the elderly, including hospitalizations and death. In Taiwan, government-funded influenza vaccination is offered to the elderly ≥65 years old. We aim to evaluate vaccine effectiveness (VE) among this group during 2023-2024 influenza season using national databases.
Methods:
A retrospective cohort study was conducted to evaluate VE among adults aged ≥65 years. Individuals were grouped by vaccination status: those vaccinated between October 2 and November 15, 2023 comprised the vaccinated group, while those without vaccination records during this period formed the unvaccinated group. The observation period began 14 days after vaccination (index date) and continued through February 15, 2024; for unvaccinated individuals, the index date was October 2, 2023. Outcome and covariate data were obtained from linked national databases. VE was estimated using adjusted logistic regression models, with sensitivity analyses using propensity score matching.
Results:
Among 4,174,655 individuals, 1,833,476 (44 %) were vaccinated. Influenza vaccination showed moderate to high effectiveness against laboratory-confirmed influenza outcomes, with adjusted VE ranging from 29.6 % (outpatient visits) to 75.2 % (severe disease). Moderate effectiveness was observed against influenza-like illness outpatient visits (VE: 21.2 %), inpatient visits (37.8 %) and all-cause mortality within 30 days (48.2 %). VE estimates increased after covariate adjustment, especially for severe outcomes. Findings were consistent in analyses using propensity score matching.
Conclusions:
Influenza vaccination was moderately to highly effective against both laboratory-confirmed influenza and influenza-like illness in elderly adults. Protection was observed across outpatient visits, hospitalizations, and mortality.
