Immunogenicity and safety of a quadrivalent inactivated influenza virus vaccine compared with a comparator quadrivalent inactivated influenza vaccine in a pediatric population: A phase 3, randomized noninferiority study

Background: Seqirus 2010 Southern Hemisphere split-virion trivalent inactivated influenza vaccine (IIV3) was associated with increased febrile reactions in children. Studies in vitro concluded that increasing concentrations of splitting agent decreased residual lipids and attenuated proinflammatory cytokine signals associated with fever. We assessed immunogenicity and safety of a quadrivalent inactivated influenza vaccine (IIV4; produced using higher concentration of splitting agent) versus a United States-licensed comparator IIV4 in healthy children aged 5-17years.

Methods: Participants (N=2278) were randomized 3:1 and stratified by age (5-8years; 9-17years) to receive IIV4 (n=1709) or comparator IIV4 (n=569). Primary objective was to demonstrate noninferiority of IIV4 versus comparator IIV4 as assessed by hemagglutination inhibition (HI) geometric mean titer (GMT) ratio (upper bound of two-sided 95% confidence interval [CI]≤1.5) and difference in seroconversion rate (upper bound of two-sided 95% CI≤10%) for all four vaccine strains. HI antibody titers were assessed at baseline and 28days postvaccination. Solicited and unsolicited adverse events were assessed during each 7- and 28-day postvaccination period, respectively.

Results: IIV4 met immunogenicity criteria for noninferiority. Adjusted GMT ratios (comparator IIV4/IIV4) for A/H1N1, A/H3N2, B/Yamagata, and B/Victoria strains were 1.01 (95% CI; 0.93, 1.09), 1.05 (0.96, 1.15), 0.89 (0.81, 0.98), and 0.92 (0.83, 1.02), respectively. Corresponding values for differences (95% CI) in seroconversion rates (comparator IIV4 minus IIV4) were -3.1 (-8.0, 1.8), 0.4 (-4.5, 5.3), -3.4 (-8.3, 1.5), and -2.0 (-6.9, 2.9). Fever rates were numerically higher, but not statistically different, with IIV4 versus comparator IIV4. No new safety signals were reported.

Conclusion: IIV4 demonstrated immunological noninferiority to the comparator IIV4 with a clinically acceptable safety profile in children aged 5-17years. Increased levels of virus splitting agent seem to have reduced fever rates observed in children with Seqirus IIV3, particularly those aged 5-8years.

Funding: Seqirus Pty Ltd; Clinicaltrials.gov identifier: NCT02545543.