title: Effectiveness of influenza vaccination in institutionalized older adults: a systematic review.
abstract: BACKGROUND
  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.
  
  
  CONCLUSIONS
  Influenza vaccination in institutionalized older adults could reduce pneumonia and death due to pneumonia or influenza. Influenza vaccination is recommended for institutionalized older adults.
authors: Department of Medicine and Geriatrics, Fung Yiu King Hospital, Hong Kong SAR, China; Division of Geriatrics, Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong SAR, China. Electronic address: tuenching@yahoo.com.hk.
authors: Tuen-Ching
authors: TC
authors: Chan
authors: Division of Infectious Disease, Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong SAR, China.
authors: Ivan
authors: I
authors: Fan-Ngai Hung
authors: Department of Medicine and Geriatrics, Fung Yiu King Hospital, Hong Kong SAR, China.
authors: James
authors: J
authors: Ka-Hay Luk
authors: Division of Geriatrics, Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong SAR, China.
authors: Leung-Wing
authors: LW
authors: Chu
authors: Department of Medicine and Geriatrics, Fung Yiu King Hospital, Hong Kong SAR, China.
authors: Felix
authors: F
authors: Hon-Wai Chan
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007252:Influenza Vaccines / Q000276:immunology*; D007251:Influenza, Human / Q000517:prevention & control*; D007326:Institutionalization; D008297:Male; D009735:Nursing Homes; D011014:Pneumonia / Q000401:mortality / Q000517:prevention & control; D014481:United States / Q000453:epidemiology
chemical_list: D007252:Influenza Vaccines
keywords: Influenza vaccination; efficacy; institutionalized older adults; meta-analysis; review