The attack rates among HIV-uninfected IIV3 recipients and their infants were 1.8 % and 1.9 % , respectively , and the respective vaccine-efficacy rates were 50.4 % ( 95 % confidence interval [ CI ] , 14.5 to 71.2 ) and 48.8 % ( 95 % CI , 11.6 to 70.4 ) .