Intervention rate ratios for influenza-like illness.

aIntracluster correlation coefficient: 0.0004 in unadjusted model (N = 938), −0.0005 in model adjusting for gender, race, ethnicity, smoking status, physical activity, and having ever received a vaccination for influenza (N = 828). bRR, rate ratio. c95% CI, 95% confidence interval. dCumulative rate ratio is the week by treatment effect which is equivalent to the hazard ratio over the study period. eSignificance level set at P<0.05.