After adjusting for bias in meta-analysis seasonal influenza vaccine remains effective in community-dwelling elderly

J Clin Epidemiol. 2014 Jul;67(7):734-44. doi: 10.1016/j.jclinepi.2014.02.009. Epub 2014 Apr 24.


Objective: To compare the performance of the bias-adjusted meta-analysis to the conventional meta-analysis assessing seasonal influenza vaccine effectiveness among community-dwelling elderly aged 60 years and older.

Study design and setting: Systematic literature search revealed 14 cohort studies that met inclusion and exclusion criteria. Laboratory-confirmed influenza, influenza-like illness, hospitalization from influenza and/or pneumonia, and all-cause mortality were study outcomes. Potential biases were identified using bias checklists. The magnitude and uncertainty of biases were assessed by expert opinion. Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated using random effects model.

Results: After incorporating biases, overall effect estimates regressed slightly toward no effect, with the largest relative difference between conventional and bias-adjusted ORs for laboratory-confirmed influenza (OR, 0.18; 95% CI: 0.01, 3.00 vs. OR, 0.23; 95% CI: 0.03, 2.04). In most of the studies, CIs widened reflecting uncertainties about the biases. The between-study heterogeneity reduced considerably with the largest reduction for all-cause mortality (I(2) = 4%, P = 0.39 vs. I(2) = 91%, P < 0.01).

Conclusion: This case study showed that after addressing potential biases influenza vaccine was still estimated effective in preventing hospitalization from influenza and/or pneumonia and all-cause mortality. Increasing the number of assessors and incorporating empirical evidence might improve the new bias-adjustment method.

Keywords: Bias adjustment; Community-dwelling elderly; Meta-analysis; Observational studies; Seasonal influenza; Vaccination.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Aged
  • Aged, 80 and over
  • Bias*
  • Cohort Studies
  • Hospitalization
  • Humans
  • Influenza Vaccines / administration & dosage*
  • Influenza, Human / epidemiology*
  • Influenza, Human / mortality
  • Influenza, Human / prevention & control
  • Meta-Analysis as Topic*
  • Observational Studies as Topic
  • Odds Ratio
  • Outcome Assessment, Health Care
  • Seasons
  • Uncertainty


  • Influenza Vaccines