RT Journal
A1 Wong K, Campitelli MA, Stukel TA, Kwong JC
T1 EStimating influenza vaccine effectiveness in community-dwelling elderly patients using the instrumental variable analysis method
JF Archives of Internal Medicine
JO Archives of Internal Medicine
YR 2012
FD March 26
VO 172
IS 6
SP 484
OP 491
DO 10.1001/archinternmed.2011.2038
UL http://dx.doi.org/10.1001/archinternmed.2011.2038
AB Background 
                  Estimates of influenza vaccine effectiveness in elderly individuals are largely from observational studies, which are susceptible to bias. Instrumental variable (IV) methods control for overt and hidden biases in observational studies.Methods 
                  We used linked health administrative databases in Ontario to examine the association between influenza vaccination and all-cause mortality among community-dwelling individuals older than 65 years for 9 influenza seasons (2000-2001 to 2008-2009). We examined the composite of hospitalization for pneumonia and influenza and all-cause mortality as a secondary outcome. We used logistic regression modeling and IV analysis to remove the effect of selection bias.Results 
                  We included 12 621 806 person–influenza seasons of observation. Logistic regression produced adjusted odds ratios of 0.67 (95% CI, 0.62-0.72) for all-cause mortality during influenza seasons and 0.85 (0.83-0.86) during post–influenza seasons when influenza is not circulating, suggesting the presence of bias. In contrast, IV analysis yielded adjusted odds ratios of 0.94 (95% CI, 0.84-1.03) during influenza seasons and 1.13 (1.07-1.19) during post–influenza seasons. For the composite of hospitalization for pneumonia and influenza and death, logistic regression produced adjusted odds ratios of 0.74 (95% CI, 0.70-0.78) during influenza seasons and 0.88 (0.87-0.90) during post–influenza seasons, whereas IV analysis produced adjusted odds ratios of 0.86 (95% CI, 0.79-0.92) and 1.02 (0.97-1.06), respectively.Conclusions 
                  Influenza vaccination is associated with reductions in the composite of hospitalizations for pneumonia and influenza and all-cause mortality during the influenza season but not mortality alone. Compared with standard modeling, IV analysis appears to produce less-biased estimates of vaccine effectiveness.