Safety and Immunogenicity of an Inactivated Quadrivalent Influenza Vaccine in Children 6 Months through 8 Years of Age

BACKGROUND: Strains of 2 distinct influenza B lineages (Victoria and Yamagata) have cocirculated in the United States for over a decade, but trivalent influenza vaccines (TIVs) contain only 1 B-lineage strain. Each season, some or most influenza B disease is caused by the B lineage not represented in that season's TIV. Quadrivalent influenza vaccines (QIVs) containing a strain from each B lineage should resolve this problem. METHODS: This was a Phase III, randomized, multicenter trial in the United States among children 6 months to <9 years of age to evaluate the safety and immunogenicity of inactivated QIV compared with inactivated control TIVs containing opposite B-lineage strains. Participants were randomized at a ratio of approximately 4:1:1 to receive QIV, TIV containing a Victoria-lineage B strain or TIV containing a Yamagata-lineage B strain. Sera were collected pre- and 28-days post-final vaccination and safety was assessed for 6 months after the last injection. RESULTS: A total of 4363 participants were enrolled. QIV induced noninferior antibody responses to all A strains and corresponding B strains compared with the control TIVs and superior antibody responses to the noncorresponding B strain in each TIV. Rates of solicited reactions and unsolicited and serious adverse events were similar in all groups. CONCLUSIONS: This study demonstrated that QIV is safe and immunogenic among children 6 months to <9 years of age. These findings, along with data from 2 other studies of this QIV in adults, suggest that QIV should offer protection against both B lineages with a safety profile similar to TIV across all ages.