Clinical Question: Is the influenza vaccine effective for preventing influenza and influenza-like illness in older patients?
Setting: Various (meta-analysis)
Study Design: Systematic review
Synopsis: The authors systematically searched multiple databases for controlled studies (e.g., randomized controlled trials, cohort studies, case-control studies) of influenza vaccines in older patients. They do not describe searching for unpublished studies. The authors included nonrandomized studies “to enhance the relevance to public-health decision-making.” Two reviewers independently applied inclusion criteria, and three independently extracted the data. They identified five randomized controlled trials, 49 cohort studies, and 10 case-control studies. The overall effect was small. Influenza vaccines were associated with a 23 percent relative reduction in influenza-like illness and no reduction in confirmed influenza. Among nursing home patients, the vaccine reduced death caused by influenza or pneumonia by 42 percent. In the randomized controlled trials, two studies with a total of 2,047 patients showed that vaccination had an overall effectiveness of 43 percent for preventing influenza-like illness, and three studies with a total of 2,217 patients showed an overall effectiveness of 58 percent for preventing influenza.
Bottom Line: Influenza vaccines prevent influenza and influenza-like illness in older patients. (Level of Evidence: 1a)