Immunogenicity and safety of 1 versus 2 doses of quadrivalent-inactivated influenza vaccine in children aged 3–8 years with or without previous influenza vaccination histories

Abstract

This study assessed the immunogenicity and safety of a quadrivalent influenza split-virion vaccine (IIV4) in children with and without prior influenza vaccination. An open-label, phase IV clinical trial was conducted in healthy children aged 3–8 years in Pizhou, Jiangsu Province, China. Children with ≥2 doses of prior influenza vaccination (Influenza Vaccination Group) and those with no prior vaccination (Influenza Vaccine-naïve Group) were given two doses of IIV4, 4 weeks apart. The primary immunogenicity endpoints were seroprotection rates (SPRs) of hemagglutination inhibition antibody 28 days after each dose against influenza A/H1N1, A/H3N2, B/Yamagata (BY), and B/Victoria (BV). Safety endpoints included adverse events (AEs) within 28 days and serious adverse events (SAEs) within 6 months. Between September 19–25, 2021, 278 participants were screened, and 240 were enrolled (120 per group). In the Influenza Vaccination Group, SPRs after the 2nd dose were 98.28%, 92.24%, 99.14%, and 87.93%, similar to those after the 1st dose (all p > .05). In the Influenza Vaccine-naïve Group, SPRs after the 2nd dose were 99.12%, 96.49%, 99.12%, and 92.11%, significantly higher than after the 1st dose (p < .001 for all strains except BY, p = .070). Most AEs were mild or moderate, with no serious AEs related to the vaccine. Children aged 3–8 years with prior influenza vaccination need only one dose of IIV4, while those without prior vaccination require two doses. ClinicalTrials.gov, the identifier is NCT05144464.

Keywords

• Inactivated influenza vaccine
• immunogenicity
• safety
• previous influenza vaccination
• 1 versus 2 doses