Immunogenicity and safety of live attenuated influenza vaccine in children aged 3-17 years in China.

(1) Background: The administration of a live attenuated influenza vaccine (LAIV) has emerged as a viable option for preventing pediatric infections. The LAIV vaccine is available in China based on efficacy results. However, LAIV immunogenicity in children aged 3-17 years old in China has not yet to be studied and reported broadly. (2) Methods: This is a substudy investigating the immunogenicity and safety of the LAIV under a Phase 3, multicentre, randomized, double-blind, placebo-controlled trial. A total of 3000 participants were enrolled in a randomized, double-blind, placebo-controlled trial, split in half between vaccine and placebo, was conducted to evaluate a single LAIV dose in this age group. Hemagglutination inhibition (HI) antibody titers and incidence of adverse events were used to evaluate immunogenicity and safety, respectively. (3) Results: Although there was no significant difference in frequencies of all solicited or unsolicited AEs, nasal congestion, headache, and muscle pain were statistically significantly more frequent in vaccine recipients as compared to placebo Seroconversions and geometric mean fold increases in HI antibody titers against all strains were significantly higher in the vaccine group than in the placebo group. (4) Conclusions: The LAIV is safe and immunogenic in Chinese children and adolescents.