[Effectiveness of influenza vaccine in the elderly. A critical review of the bibliography]

Abstract

Background: The acceptance of influenza vaccine has been slow as doubts about its effectiveness persist. The goal of this study is to review the existing evidence on influenza vaccine effectiveness in preventing pneumonia and influenza hospitalizations in non institutionalized elderly.

Methods: We have conducted a search in MEDLINE, including a period between 1984 and 1994, and of cross references, between 1980 and 1994. Twelve studies have been identified and valued independently by the authors. The results are combined through a graphic representation and the quantitative method proposed by Woolf.

Results: Four studies have been excluded; two, because they did not satisfy the comparability principle; one, because it was a publication already published; and one because of small numbers. According to the graphic method, influenza vaccine prevents between 29 and 51 percent of pneumonia and influenza hospitalizations in the non institutionalized elderly. When results are integrated by the quantitative method, the odds ratio is 0.63 (CI 95%, 0.54 to 0.72). The percentage of pneumonia and influenza hospitalizations prevented by the influenza vaccine equals 37.40% (CI 95%, 27.81% to 45.72%) in the vaccinated.

Conclusions: The annual influenza immunization of those 65 years old or older is an effective primary prevention strategy.