1. Quadrivalent influenza vaccine (QIV) was found to have efficacy of approximately 60% in protecting children from influenza.
2. QIV protection was more efficacious against moderate-to-severe influenza, with efficacy over 70%. Seroprotection rates after vaccination was over 95% for all four strains.
Evidence Rating Level: 1 (Excellent)
Study Rundown: This phase 3 trial demonstrated the safety and efficacy of quadrivalent influenza vaccine (QIV) in children 3 to 8 years old. In this study, QIV was found to be approximately 60% effective against influenza infection of any severity, and more than 70% effective against moderate-to-severe influenza infections, thus highlighting the efficacy in reducing clinically significant events. The study results are adequately powered with more than 5000 children enrolled in three parts of the world. Follow up rate was also high, with 95% of samples from children with suspected cases obtained and analyzed. The current study analyzed only one flu season. It did not address whether this quadrivalent vaccine is any more advantageous than the more widely used trivalent vaccine, as there were only 2 cases of B/Yamagata influenza. A quadrivalent vaccine may be of greater value during seasons in which both B lineages are circulating, or if there is a shift from one lineage to another during the same season. Future studies are needed to address this question.
The study was sponsored by GlaxoSmithKline. The sponsor was involved in all stages of the study conduct and analyses of data.
In-Depth [randomized controlled trial]: This study assessed the safety and efficacy of quadrivalent influenza vaccine (QIV) in children aged 3 to 8. The vaccine contained the hemagglutinin antigens from the following four strains: A/H1N1, A/H3N2, B/Victoria, and B/Yamagata. Children were assigned in a 1:1 ratio to either receive QIV or hepatitis A vaccine as control. Primary end point was influenza A or B confirmed by rt-PCR. Secondary end point was rt-PCR confirmed, moderate-to-severe influenza.
In the total vaccinated cohort, 62 children in the QIV group (2.4%) and 148 in the control group (5.7%) had rt-PCR-confirmed influenza, reflecting a vaccine efficacy of 59.3% (95% confidence interval [CI], 45.2 to 69.7). In the per-protocol cohort, 58 children in the QIV group (2.4%) and 128 in the control group (5.3%) had rt-PCR-confirmed influenza, reflecting a vaccine efficacy of 55.4% (95% CI, 39.1 to 67.3). The vaccine had higher efficacies against moderate-to-severe influenza, with efficacy of 74.2% (97.5% CI, 51.5 to 86.2) in the total vaccinated cohort and 73.1% (97.5% CI, 47.1 to 86.3) in the per-protocol cohort.
In an immunogenicity analysis, seroprotection rates against each strain was more than 95% after vaccination. At 6 months post immunization, seroprotection rates were higher than 90% against A/H3N2 and B/Yamagata, and higher than 80% against A/H1N1 and B/Victoria. Safety end points did not differ between the QIV group and the control group.
By Xiaozhou Liu and Xu Gao
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