Significant reductions in the incidence rate of upper respiratory tract infection ( URTI ; 33 % , P = 0.002 ) , the number of days with URTI symptoms ( mean difference : -21.0 , 95 % confidence interval ( CI ) : -35.9 , -6.0 , P = 0.006 ) and the incidence rate of absence from preschool ( 30 % , P = 0.007 ) were observed in the active group compared with the placebo .