TY  - JOUR
T1  - TO rule out confounding, observational studies of influenza vaccine need to include analyses during the “preinfluenza period”—reply
AU  - Fisman DN
Y1  - 2007/07/23
N1  - 10.1001/archinte.167.14.1554
JO  - Archives of Internal Medicine
SP  - 1554
EP  - 1555
VL  - 167
IS  - 14
N2  - 
We appreciate the comments of Jackson and colleagues regarding possible residual confounding by health status as an explanation for the protection provided by influenza vaccination against death in our study.1 Confounding and biases represent ever-present threats to validity for even the best thought-out observational research.2 We controlled for numerous potential confounders, including health status, nursing home residence, and severity of illness on admission in multivariable models, and the observed protective effect of influenza vaccination remained robust. Furthermore, we included only hospitalized individuals with pneumonia. The implicit exclusion of vaccinated individuals at low risk of pneumonia-related hospitalization makes a “healthy vaccine effect” unlikely.

SN  - 0003-9926
M3  - doi: 10.1001/archinte.167.14.1554
UR  - http://dx.doi.org/10.1001/archinte.167.14.1554
ER  -