Safety and Immunogenicity of Cell-Based Quadrivalent Influenza Vaccine: A Randomized Trial.

Young children are at increased risk for influenza-related complications. Safety and immunogenicity of a cell-based quadrivalent inactivated influenza vaccine (QIVc) was compared with a US-licensed vaccine (QIV) in children aged 6 through 47 months. A phase 3, randomized, observer-blind, comparator-controlled, multicenter study was conducted during Northern Hemisphere 2019-2020 influenza season. Children were randomized 2:1 to QIVc or QIV and received 1 or 2 doses of the vaccine, depending upon influenza vaccination history. Safety was assessed for 180 days after last vaccination and sera were collected before and 28 days after last vaccination to measure antibody titers in hemagglutination inhibition and microneutralization assays. Noninferiority criteria were met if the upper bounds of the 2-sided 95% confidence interval (CI) for the geometric mean titer ratio (QIV:QIVc) did not exceed 1.5 and for seroconversion rate difference (QIV-QIVc) did not exceed 10% for the 4 virus strains. Immunogenicity was evaluated in 1092 QIVc and 575 QIV subjects. Success criteria were met for all vaccine strains. Geometric mean titer ratios (upper bound 95% CI) were A/H1N1, 0.73 (0.84); A/H3N2, 1.04 (1.16); B/Yamagata, 0.73 (0.81); and B/Victoria, 0.88 (0.97). Seroconversion differences (upper bound 95% CI) were -11.46% (-6.42), 3.13% (7.81), -14.87% (-9.98), and -5.96% (-1.44) for A/H1N1, A/H3N2, B/Yamagata, and B/Victoria, respectively. Rates of adverse events were similar between the 2 groups with no serious adverse events related to vaccination. QIVc was well-tolerated and immune responses were similar to a US-licensed QIV in children 6 through 47 months of age.