All 1950 participants received 1 intramuscular dose of Fluzone Quadrivalent vaccine during Visit 1. For participants, for whom 2 doses of influenza vaccine were recommended per Advisory Committee on Immunization Practices (ACIP) guidance, the second dose of Fluzone Quadrivalent vaccine (of the same volume as the first dose) was administered during Visit 2 (28 days after Visit 1).

Solicited adverse event (AE) information was collected for 7 days after each vaccination, unsolicited AE information was collected from Visit 1 to Visit 2 or to Visit 3 for participants receiving 2 doses of study vaccine. Serious adverse event (SAE) information was collected for 28 days after each vaccination.

Immunogenicity was evaluated in a planned subset of 1600 randomly selected participants prior to vaccination on Day 0 (Visit 1) and at Day 28 after the final vaccination.

Results

Pediatric Infectious Disease Journal published the results of this study in March 2019.

Results: The study included 1950 children. Noninferiority in the rate of fever was demonstrated for the full dose versus the half dose of IIV4 (difference in rate = 0.84%; 95% confidence interval, -2.13% to 3.80%). Solicited reactions and unsolicited adverse events were similar between the dose groups. No vaccine-related serious adverse events were reported. Noninferiority of both hemagglutination inhibition geometric mean titers and seroconversion rates was demonstrated for all 4 vaccine strains for the full dose versus the half dose.

Conclusions: In children 6-35 months of age, a full dose of IIV4 was immunogenic and had a safety profile comparable to that of a half dose, with no new safety concerns observed.