Efficacy of a Cell-Culture-Derived Quadrivalent Influenza Vaccine in Children.

Background Cell-culture-derived influenza vaccines may enable a closer antigenic match to circulating strains of influenza virus by avoiding egg-adapted mutations. Methods We evaluated the efficacy of a cell-culture-derived quadrivalent inactivated influenza vaccine (IIV4c) using a Madin-Darby canine kidney cell line in children and adolescents 2 to less than 18 years of age. During three influenza seasons, participants from eight countries were enrolled in an observer-blinded, randomized clinical trial comparing IIV4c with a noninfluenza vaccine (meningococcal ACWY). All the participants received a dose of a trial vaccine. Children 2 to less than 9 years of age without previous influenza vaccination who were assigned to the IIV4c group received a second dose on day 29; their counterparts who were assigned to the comparator group received placebo. Participants were followed for at least 180 days for efficacy and safety. The presence of influenza virus in nasopharyngeal swabs from participants with influenza-like illness was confirmed by reverse-transcriptase-polymerase-chain-reaction assay and viral culture. A Cox proportional-hazards model was used to evaluate the efficacy of IIV4c as measured by the first occurrence of laboratory-confirmed type A or B influenza (primary end point). Results 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. Conclusions IIV4c provided protection against influenza in healthy children and adolescents across seasons, regardless of previous influenza vaccination. (Funded by Seqirus; EudraCT number, 2016-002883-15; ClinicalTrials.gov number, NCT03165617.).