Flu vaccination effectiveness in elderly

[Guest guest]

Interesting study which challenges the notion that vaccinating the elderly decreases mortality from influenza. Haven't read the whole study but the take home is that the bias inherent to observational studies tend to show effectiveness whereas addressing the bias removes the apparent effectiveness. (Those getting the shots are those trying to take care of themselves in the first place!) Seitz, DC Tuality Physicians 730-D SE Oak St Hillsboro, OR 97123 (503)640-3724ONLINE FIRST

Estimating Influenza Vaccine Effectiveness in

Community-Dwelling Elderly Patients Using the Instrumental Variable Analysis

Method

Kenny Wong, MPH;

A. Campitelli, MPH; Thérèse

A. Stukel, PhD;

C. Kwong, MD, MSc

Arch

Intern Med. 2012;172(6):484-491. doi:10.1001/archinternmed.2011.2038

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.