The efficacy and safety of a quadrivalent live attenuated influenza nasal vaccine in Japanese children: A phase 3, randomized, placebo-controlled study

BackgroundVaccination is the primary method of preventing influenza infection and complications in young children. We evaluated the efficacy and safety of a single dose of MEDI3250 (intranasal, quadrivalent, live attenuated influenza vaccine) in healthy Japanese children during the 2016/17 influenza season.MethodsIn this multicenter, randomized, double-blind, phase 3 study (jRCT2080223345), participants aged 2–18 years received MEDI3250 or placebo (2:1), stratified by age (2–6 years, 7–18 years). The primary and secondary endpoints were the incidence of confirmed symptomatic onset of influenza caused by a circulating wild-type strain or by a vaccine-matched strain, respectively. Safety outcomes included the incidence of adverse events (AEs) and vaccine-related AEs.ResultsOverall, 910 participants received MEDI3250 (n = 608) or placebo (n = 302). For the primary endpoint (regardless of the influenza subtype), the incidence of influenza onset was 25.5 % (MEDI3250) and 35.9 % (placebo); relative risk reduction, 28.8 % (95 % confidence interval, 12.5 %, 42.0 %). For the secondary endpoint (vaccine-matched strain), the incidence was 10.9 % (MEDI3250) and 17.2 % (placebo); relative risk reduction, 36.6 % (95 % confidence interval, 6.5 %, 56.8 %). Solicited AEs occurred in 67.6 % (MEDI3250) and 63.6 % (placebo). Most events were mild; nasal discharge was most common (59.2 % [MEDI3250] and 52.6 % [placebo]). Unsolicited AEs occurred in 36.0 % (MEDI3250) and 33.1 % (placebo). The most common unsolicited vaccine-related AE was diarrhea (2.3 %, both groups).ConclusionsMEDI3250 had a greater preventive effect against influenza onset in Japanese children than placebo; no new safety signals were observed relative to previous clinical and post-marketing studies of MEDI3250.