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

INTRODUCTION: 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. METHODS: 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. RESULTS: 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. CONCLUSION: Influenza vaccination in institutionalized older adults could reduce pneumonia and death due to pneumonia or influenza. Influenza vaccination is recommended for institutionalized older adults.

Efficacy of trivalent seasonal influenza vaccination in reducing mortality and hospitalization in Chinese nursing home older adults.

OBJECTIVE: To examine the clinical efficacy of the trivalent seasonal influenza vaccination among Chinese older adults residing in a nursing home. DESIGN: A 12-month prospective cohort study. Participants were divided into 2 groups based on their own choice on vaccination of trivalent seasonal influenza vaccine: vaccinated group and unvaccinated group. SETTING: Fifty-eight nursing homes in Hong Kong. PARTICIPANTS: A total of 1859 older adults residing in a nursing home. MEASUREMENTS: All-cause mortality, pneumonia-related mortality, all-cause hospitalization, and pneumonia-related hospitalization. RESULTS: A total of 1859 older adults residing in a nursing home were included: 1214 (65.3%) in the vaccinated group and 645 (34.7%) in the unvaccinated group. At 12 months of study, for all-cause mortality, 14.6% (177 of 1214) of the vaccinated group and 20.2% (130 of 645) of the unvaccinated group had died (P < .001). Multivariate analysis showed the hazard ratio for the vaccinated group was 0.72 (95% confidence interval [CI]: 0.54-0.95; P < .01). For pneumonia-related mortality, 9.4% (114 of 1214) of the vaccinated group and 12.7% (82 of 645) of the unvaccinated group died (P = .033). Multivariate analysis showed the hazard ratio for the vaccinated group was 0.80 (CI: 0.62-0.98; P < .05). The median number of all-cause hospitalizations per 1000 person-months was 55 (0-111) for the vaccinated group and 55 (0-167) for the unvaccinated group (P < .01). The median number of pneumonia-related hospitalizations per 1000 person-months was 0 (0-55) for the vaccinated group and 0 (0-111) for the unvaccinated group (P < .01). CONCLUSIONS: Vaccination of trivalent seasonal influenza vaccine in Chinese nursing home older adults significantly reduced all-cause and pneumonia-related mortality and hospitalization.