In the intention-to-treat analysis , 228 participants in the IIV3-HD group ( 1.4 % ) and 301 participants in the IIV3-SD group ( 1.9 % ) had laboratory-confirmed influenza caused by any viral type or subtype associated with a protocol-defined influenza-like illness ( relative efficacy , 24.2 % ; 95 % confidence interval [ CI ] , 9.7 to 36.5 ) .