Obesity was named as a risk factor for severe H1N1 influenza during the pandemic. What about for influenza in general?
Kwong et al analyzed community survey data in Ontario over 12 influenza seasons, 1996-2008. Severe obesity (BMI >= 35) carried an odds ratio of 2.1 for respiratory hospitalization during flu season. In those with no other identifiable risk factors besides severe obesity, the odds ratio was 5 (compared to non-obese controls). "Ordinary" obesity (BMI 30-34.9) had an odds ratio of 1.45. Authors suggest the obese be targeted more assertively in vaccination campaigns.
sept 1. Clin Infect Dis 2011;53:413-421.