OBJECTIVES/GOALS: There is an excess risk of upper respiratory infection (URI) among Black and Mexican-American children in the US. Factors that underpin these disparities are largely unknown. We evaluated the extent to which socioeconomic status (SES), serum cotinine, obesity, and household size explained the association between race/ethnicity and URI. METHODS/STUDY POPULATION: We studied children, 6-17 years of age, who identified as Black, Mexican-American, or White in the National Health and Nutritional Examination Survey (2007-2012). URI was defined as a self-reported cough, cold, phlegm, runny nose, or other respiratory illness (excluding hay fever and allergies) in the past 7 days. The proportion of the association between race/ethnicity and URI explained by SES, serum cotinine, obesity, and household size was estimated as the average causal mediation effect (i.e., the indirect effect of race/ethnicity via the mediator) divided by the total effect of race/ethnicity. The average causal mediation effect was derived from survey weighted logistic regression models adjusted for age and sex. RESULTS/ANTICIPATED RESULTS: Black children were nearly 40% and Mexican American children were ~60% more likely to report a URI than those who identified as White (OR, 1.37; 95% CI, 1.06-1.77 and OR, 1.61; 95% CI, 1.21-2.13, respectively). Lower SES explained ~25% of the association between Black and Mexican American identity and URI (percent mediated 24.7; 95% CI, 23.0-26.6 and 26.1; 95% CI, 24.2-28.2, respectively). Obesity explained ~7% of the association between Black and Mexican-American identity and URI (percent mediated, 7.6; 95% CI, 7.3-8.0 and percent mediated, 6.7; 95% CI, 6.4-6.9, respectively). Nicotine exposure explained 8% of the association between Black identity and URI (percent mediated, 7.9; 95% CI, 5.6-10.1). DISCUSSION/SIGNIFICANCE: Lower SES explained a quarter of the association between race/ethnicity and URI. Low SES is a broad concept that may work through different mechanisms to lead to disparities in URI by race/ethnicity. Future research is needed to better understand these mechanisms and to identify modifiable aspects that can serve as targets for intervention.