BACKGROUND:

For children aged < 3 years, a half dose of inactivated influenza vaccine (7.5 μg hemagglutinin/strain) has been used for more than 30 years, but several studies indicate that a full dose (15 μg hemagglutinin/strain) can be used in this population without increasing the rate of fever or other reactions. Here we compare the safety and immunogenicity of full and half doses of quadrivalent split-virion inactivated influenza vaccine (IIV4) in children aged 6 to 35 months.

METHODS:

In this phase IV, randomized, observer-blinded, multi-center study, healthy children aged 6 to 35 months were randomized 1:1 to be vaccinated with a half or full dose of IIV4 (NCT02915302). The primary objective was to demonstrate that the rate of any fever (≥ 38.0°C) up to 7 days after a full dose of IIV4 was non-inferior to the rate of fever after a half dose.

RESULTS:

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

CONCLUSIONS:

In children aged 6 to 35 months, 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.