Influenza Vaccine Effectiveness in Preventing Hospitalizations and Deaths in Persons 65 Years or Older in Minnesota, New York, and Oregon: Data from 3 Health Plans

Abstract

This study developed methods and determined the impact of influenza vaccination on elderly persons in 3 large health plans: Kaiser Permanente Northwest, HealthPartners, and Oxford Health Plans. Data for the 1996-1997 and 1997-1998 seasons were extracted from administrative databases. Subjects were health plan members > or = 65 years old. Comorbid conditions collected from the preceding year were used for risk adjustment with logistic regression. The virus-vaccine match was excellent for year 1 and fair for year 2. Both years, during peak and total periods, vaccination reduced all causes of death and hospitalization for pneumonia and influenza: hospitalizations were reduced by 19%-20% and 18%-24% for years 1 and 2, respectively, and deaths were reduced by 60%-61% and 35%-39% for the same periods. These results show that all elderly persons should be immunized annually for influenza. The methods used in this study are an efficient cost-effective way to study vaccine impact and similar questions.

A nested case-control study of influenza vaccination was a cost-effective alternative to a full cohort analysis

“…These findings agree with a recent large study among elderly members of three HMOs followed during the 1996/97 and 1997/98 influenza A epidemics [28]. The estimate of 159 persons that need to be vaccinated to prevent one serious outcome was somewhat higher than in the large HMO study (102 persons).…”

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“…According to a meta-analysis of 20 cohort studies, published between 1974 and 1992, the pooled estimate of the efficacy of the vaccine was: 56% for prevention of respiratory illness; 53% for prevention of pneumonia; 50% for prevention of hospitalisation overall; and 68% for prevention of death [274]. Recent large cohort studies of the elderly in the community have confirmed these findings, demonstrating efficacy rates between 20-80% in the prevention of hospitalisation for influenza and pneumonia, 40% in the prevention of congestive heart failure, and 40-70% in the prevention of death overall [275][276][277][278][279][280]. There are also data indicating that the absolute risk reduction is 2-5 times higher among high-risk persons than among healthy elderly persons [281].…”

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