Using a conceptual framework adapted from Diderichsen et al. (14) , we systematically considered possible sources of disparities during an infl uenza pandemic by examining the following 3 levels at which underlying socioeconomic or racial/ethnic differences could lead to disparities in illness or death: 1) likelihood of being exposed to the infl uenza virus; 2) likelihood of contracting infl uenza disease, if exposed; and 3) likelihood of receiving timely and effective treatment after infl uenza disease has developed. To explore socioeconomic and racial/ethnic disparities at each level, we searched the literature for relevant fi ndings based on population-based national data (Figure, Table) .