Evaluation of Waning Immunity at 6 Months after Both Trivalent and Quadrivalent Influenza Vaccination in Korean Children Aged 6-35 Months.

Persistence of antibodies at 6 months was more favorable against the influenza A strains than against the B strains. Persistence of antibodies to additional B strain at 6 months was superior in the quadrivalent vaccine group. The immunity of primed children with different B strains was not superior to that of the unprimed group with another B strain.