The mortality rate ratio ( MRR ) comparing VAS versus placebo recipients was 0.91 ( 95 % confidence interval 0.59-1 .41 ) and differed significantly between boys ( MRR 1.92 [ 0.98-3 .75 ] ) and girls ( MRR 0.45 [ 0.24-0 .87 ] ) ( P = .003 for interaction between VAS and gender ) .