This Phase 3/4, randomized, observer-blind, multi-center, stratified study evaluated the efficacy, safety, and immunogenicity of a cell-derived quadrivalent subunit influenza virus vaccine (Seqirus QIVc) compared to a non-influenza comparator vaccine in healthy male and female participants between 2 to <18 years of age.

A total of 4514 children/teens were randomized, receiving either QIVc or the non-influenza comparator vaccine. The comparator was (meningococcal [Groups A, C, W-135, and Y] oligosaccharide diphtheria CRM197 conjugate vaccine [Men ACWY]).

Randomized enrollment was stratified in a 1:1 ratio via an Interactive Response Technology (IRT) system which assigned the participants into two age cohorts: 2 to <9 years of age and 9 to <18 years of age. Subjects between 2 to <9 years of age were further stratified by previous influenza vaccine status ("previously vaccinated" or "not previously vaccinated").

Results

On October 14, 2021, The New England Journal of Medicine published the results of this study.  Between 2017 and 2019, a total of 4514 participants were randomly assigned to receive IIV4c or the meningococcal ACWY vaccine. Laboratory-confirmed influenza occurred in 175 of 2257 participants (7.8%) in the IIV4c group and in 364 of 2252 participants (16.2%) in the comparator group, and the efficacy of IIV4c was 54.6% (95% confidence interval [CI], 45.7 to 62.1). Efficacy was 80.7% (95% CI, 69.2 to 87.9) against influenza A/H1N1, 42.1% (95% CI, 20.3 to 57.9) against influenza A/H3N2, and 47.6% (95% CI, 31.4 to 60.0) against influenza B. IIV4c showed consistent vaccine efficacy in subgroups according to age, sex, race, and previous influenza vaccination. The incidences of adverse events were similar in the IIV4c group and the comparator group.

Flucelvax Quadrivalent proved absolute efficacy data indicating that it was effective and produced a sufficient immune response against influenza in children and adolescents between ≥2 to <18 years of age over three influenza seasons in the Southern (2017) and Northern (2017/18 and 2018/19) Hemispheres, compared to a non-influenza comparator. This represents the first absolute efficacy study of a cell-based influenza vaccine in this population.