The efficacy of influenza vaccine in elderly persons. A meta-analysis and review of the literature

OBJECTIVE

To quantify the protective efficacy of influenza vaccine in elderly persons.

DATA SOURCES

A MEDLINE search was done using the index terms influenza vaccine, vaccine efficacy, elderly, mortality, hospitalized, and pneumonia. Appropriate references in the initially selected articles were also reviewed.

STUDY SELECTION

Only cohort observational studies with mortality assessment were included in the meta-analysis. In addition, 3 recent case-control studies, 2 cost-effectiveness studies, and 1 randomized, double-blind, placebo-controlled trial were reviewed.

DATA EXTRACTION

Vaccine and epidemic virus strains, age and sex of patients, severity of illness, patient status, and study design were recorded. Upper respiratory illness, hospitalization, pneumonia, and mortality were used as outcome measures.

DATA SYNTHESIS

In a meta-analysis of 20 cohort studies, the pooled estimates of vaccine efficacy (1-odds ratio) were 56% (95% Cl, 39% to 68%) for preventing respiratory illness, 53% (Cl, 35% to 66%) for preventing pneumonia, 50% (Cl, 28% to 65%) for preventing hospitalization, and 68% (Cl, 56% to 76%) for preventing death. Vaccine efficacy in the case-control studies ranged from 32% to 45% for preventing hospitalization for pneumonia, from 31% to 65% for preventing hospital deaths from pneumonia and influenza, from 43% to 50% for preventing hospital deaths from all respiratory conditions, and from 27% to 30% for preventing deaths from all causes. The randomized, double-blind, placebo-controlled trial showed a 50% or greater reduction in influenza-related illness. Recent cost-effectiveness studies confirm the efficacy of influenza vaccine in reducing influenza-related morbidity and mortality and show that vaccine provides important cost savings per year per vaccinated person.

CONCLUSION

Despite the paucity of randomized trials, many studies confirm that influenza vaccine reduces the risks for pneumonia, hospitalization, and death in elderly persons during an influenza epidemic if the vaccine strain is identical or similar to the epidemic strain. Influenza immunization is an indispensable part of the care of persons 65 years of age and older. Annual vaccine administration requires the attention of all physicians and public health organizations.

Influenza virus vaccine: a need for emphasis

Each year, there are more than 20,000 influenza associated deaths during influenza virus epidemics. There is an increase in hospital admission for patients with pneumonia, exacerbation of chronic obstructive pulmonary disease, croup, and congestive heart failure, and an increase in school and industrial absenteeism. Yet only 30% of the high-risk target population receives influenza vaccination annually. Health care providers and patients are reluctant to use vaccine despite its generally excellent record of safety and its approximately 70% efficacy when vaccine and epidemic strains match. The continuing change in antigenic composition of the influenza A virus and waning immunity requires annual vaccination. Vaccine composition and target groups are reviewed. Strategies for improving vaccine usage are emphasized.