Influenza: a preventable lethal disease.

Abstract

NFLUENZA and pneumonia are major health problems in older people. Influenza and pneumococcal vaccination have made a significant impact on preventing acute respiratory illness (ARI) and related complications that lead to hospitalization and death (1). However, barriers to annual vaccination in subpopulations of very high-risk older adults result in low vaccination rates in these populations. The article by Menec and colleagues (2) reports a comparison of hospitalization and death rates that were due to recognized complications of influenza in three subsamples of older people defined by their living environment and related risk of contracting influenza. Although residents of seniors’ housing and nursing homes who were hospitalized were older and included more women than hospitalized seniors from the community at large, there was no difference in comorbidities or complications. Rates of hospitalization and death related to pneumonia and influenza, chronic lung disease, and acute respiratory diseases were higher during the influenza season compared with the fall season in three settings including nursing homes, seniors’ apartments, and the community at large. These results suggest that differences in hospitalization rates among the three groups may be due to the environment and related functional status of the older adult rather than health status as it relates to risk for complicated influenza illness. Older people living in seniors’ housing, where congregate meals are often provided, had a higher risk of being hospitalized or dying of an ARI during the influenza season compared with independent community-dwelling older people even though vaccination rates appeared to be similar. Hospitalization and mortality rates in the nursing home population were similar to those for people living in seniors’ housing, but vaccination rates of 30‐60% in the latter group appeared to be lower than in the nursing home, where targeted programs have increased vaccination rates to over 80%. This study identifies the subpopulation of older people who live in seniors’ housing where functional dependence and need for transportation to a vaccination center may be a barrier to annual influenza vaccination. Because this population appears to be at higher risk of complications of influenza illness, targeted programs that provide accessible vaccination would be of great benefit for preventing hospitalization and death during the influenza season. Moreover, preventing hospitalization in frail older people also reduces the risk of increased disability and further loss of functional independence that may lead to nursing home placement following hospitalization. These human and financial costs are often not captured in health care databases of hospitalizations and deaths. Increasing vaccination rates in identified high-risk subpopulations of older adults will have a significant impact on the overall cost-effectiveness of influenza vaccination programs. Previous studies have shown that influenza vaccine efficacy is only 50‐60% for preventing influenza illness and may be as low as 23% in persons aged 70 years and older, as documented in the one published randomized trial of influenza vaccination (3). However, influenza vaccine efficacy is significantly higher for preventing influenza-related hospitalizations and death. Studies of vaccine efficacy are limited because of the required documentation of serologically confirmed influenza illness. Most studies report influenza vaccine effectiveness based on a clinical diagnosis and do not document seroconversion to influenza. These studies show rates of 29‐40% for the prevention of hospitalization for all respiratory conditions (4) and similar rates for pneumonia and influenza hospitalizations and make a strong case for influenza vaccination (5‐12). These effectiveness rates are impressive considering that they include outcomes of ARI caused by all pneumonia-causing pathogens during the influenza season and also make the case for targeted interventions in very high-risk subpopulations of older people who may be undervaccinated. Although some of these outcomes may be the result of bacterial pathogens complicating influenza illness, a variety of viral pathogens, including respiratory syncytial viruses and parainfluenza viruses, cocirculate during the influenza season and cause influenzalike illness that is clinically indistinguishable from influenza. The extended benefit of influenza vaccination includes the prevention of exacerbations of congestive heart failure during the influenza season ( � 30%) and an approximate 50% reduction in myocardial infarction and sudden cardiac death (13) as well as strokes (14). Thus, there is mounting evidence of the expanded benefits of influenza vaccination for the prevention of hospitalization in older people. Our continued efforts to find new ways of preventing influenza will result in significant health benefits to older people and a health system in crisis with the increasing health care needs of an aging population.