The rate of exacerbations was reduced by 47 % ( 95 % confidence interval [ CI ] , 29 to 61 ) among patients receiving intravenous mepolizumab and by 53 % ( 95 % CI , 37 to 65 ) among those receiving subcutaneous mepolizumab , as compared with those receiving placebo ( P < 0.001 for both comparisons ) .