| Summary: | 碩士 === 國立中興大學 === 微生物暨公共衛生學研究所 === 99 === The elderly have been considered as the priority group for vaccination, as the influenza is apt to cause illness, which is significant in terms of mortality and morbidity in that population . In Taiwan, the free influenza vaccination program began in October 1998 targeted at the high-risk elderly population and it was later on recommended for all adults aged ≥ 65 years old in Taiwan since 2001.Previous study suggested that the free vaccination program in Taiwan significantly reduced the influenza-related mortality in the elderly. The current study is aimed to understand the effect of vaccination program on the influenza illness in the elderly based on 240,000 random sample population from the National Health Insurance Research Database (NHIRD). Multivariate poisson regression was used to obtain rate ratio after adjusting potential confounding factors and using different statistical methods to model the secular trend of influenza-associated illness. Influenza illness was defined according to The International Classification of Disease, Ninth Revision, Clinical Modification (ICD-9-CM) cdoe,487, and the vaccination status was also extracted from the database. The person aged in 65-74 years old(RR=1.3; 95% CI,1.23-1.35), female(RR=1.1; 95% CI, 1.08~1.13), with co-morbidity disease (RR=1.3; 95% CI, 1.08-1.13) were the risk factors with higher incidence of acquiring influenza based on the multiple poisson regression model. Compared with the year before the implementation of universal vaccination program, the years after universal vaccination program showed significant reduction of out-patient
visit rate in the elderly by 31% (RR=0.69; 95%CI, 1.26-1.35).When vaccination rate increased 1%, out-patient visit reduced four cases per 1,000 people (AR=0.004; 95%CI, 0.001~0.007) and hospitalization reduced twelve cases per 1,000 people (AR=0.012; 95%CI, 0.001~0.033).When influenza vaccine strain, particularly H3N2 (RR=0.95;95%CI,0.91-0.99) and B (RR=0.96;95%CI,0.94-1) matched with the wild type strain also significantly reduced out-patient visit rate, but not H1N1. Only vaccine B strain matched with the wild type strain significantly reduced hospitalization rate (RR=0.91;95%CI,0.83-0.99).
In the individual study of vaccine effectivenesss, vaccination significant reduce P&I hospitalization (Vaccine effectiveness=31~51%) and revaccination also significant reduce P&I hospitalization(Vaccine effectiveness=17~22%). No vaccine effectiveness to against influenza out-patient visit in the individual study.
In summary, the implementation of universal vaccination program significant reduced the out-patient visit rate of influenza illness in the elderly.When vaccine strain mismatch, increased vaccination rate reached 75% , the vaccine effectiveness as good as vaccine strain match and vaccination rate was 50%.Revaccination significant reduce P&I hospitalization in individual study in Taiwan.
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