Effectiveness of influenza vaccination in institutionalized older adults: a systematic review

Influenza infection is common among institutionalized older adults. Many nonrandomized observational studies on influenza vaccination suggested that it could reduce influenza-related hospitalizations and mortality in institutionalized older adults. Criticism regarding the effectiveness of influenza vaccine estimated by nonrandomized observational studies include the frailty selection bias and use of nonspecific outcome, such as all-cause mortality.

We conducted a systematic review of studies of influenza vaccination in institutionalized older adults to determine the effects on clinical outcomes. We searched for studies from 3 databases from 1946 to June 2013 assessing effectiveness against influenza infection. We selected studies with good comparability between vaccine group and control group. We expressed vaccine effectiveness (VE) as a proportion, using the formula VE = 1-relative risk or 1-odds ratio. We focused on the following outcomes: influenza-like illness (ILI), laboratory confirmed influenza, hospitalizations due to ILI, or pneumonia and death due to influenza or pneumonia. We did not include all-cause mortality.

Eleven studies that satisfied the inclusion criteria were identified, representing 11,262 institutionalized older adults. After meta-analysis, we found a significant reduction in pneumonia (VE: 37%, 95% confidence interval [CI]: 18%-53%, P = .001) and death due to pneumonia or influenza (VE: 34%, CI: 10%-53%, P = .01). There was no significant heterogeneity between studies. There was no significant publication bias.

Influenza vaccination in institutionalized older adults could reduce pneumonia and death due to pneumonia or influenza. Influenza vaccination is recommended for institutionalized older adults.