Vaccines for Preventing Influenza in Older Patients
Are influenza vaccines safe and effective in persons 65 years and older?
According to data obtained primarily from poor-quality observational studies, influenza vaccination in older persons living in long-term care facilities appears to prevent approximately 45 percent of pneumonia cases, hospital admissions, and influenza-related deaths. In older persons living in the community, influenza vaccination prevents about 25 percent of hospitalizations from influenza or respiratory illness. The vaccines appear to be safe.
The authors of this review identified 71 case-control studies, cohort studies, and randomized controlled trials (RCTs) assessing the effectiveness of influenza vaccination against influenza or influenza-like illness; 64 of these studies addressed vaccine effectiveness in older persons.
There were five RCTs addressing vaccine effectiveness, with about 5,000 observations. Because vaccine type, setting, and outcomes were different in each study, conclusions were limited. A meta-analysis of two of these trials with a total of 2,567 patients showed that inactivated vaccines were more effective than placebo against influenza-like illness and influenza in community settings where there is a high viral circulation (vaccine effectiveness [VE] = 43 percent; 95% confidence interval [CI], 21 to 58 percent); pooled data from three RCTs showed that the vaccines were effective against influenza (VE = 58 percent; 95% CI, 34 to 73 percent).
Vaccines appear to be safe. Based on pooled data from four RCTs, local adverse events such as tenderness and sore arm were significantly more common with vaccine than with placebo; however, differences in systemic side effects were not statistically significant between the two groups.
In the cohort studies, healthier patients with better access to health care services may have received the vaccination preferentially, making the comparison groups different at baseline and overestimating the effectiveness of the vaccine. Likewise, the benefits for all-cause mortality found only in observational studies may reflect differences between vaccinated and nonvaccinated groups rather than a true effect. Evidence from RCTs, in which bias is reduced, is limited because of the relatively small total number of patients studied. Because of universal recommendations for influenza vaccination in older persons, it is unlikely that a randomized placebo-controlled trial will be performed to provide the high-quality evidence required.
Overall, these results support the conclusion that vaccination benefit is maximized if those at greatest risk for influenza complications are successfully targeted for vaccination. The effectiveness of vaccination in older persons living in community-based settings was more modest. The Advisory Committee on Immunization Practices recommends annual influenza vaccination for the following groups: persons at high risk for influenza-related complications and severe disease, including children six to 59 months of age, pregnant women, persons 50 years or older, and persons of any age with certain chronic medical conditions; and those who live with or care for persons at high risk.1