Immunogenicity and Safety of Quadrivalent Live Attenuated Influenza Vaccine in Children

A randomized, double-blind study was conducted to demonstrate the immunologic noninferiority of an investigational quadrivalent live attenuated influenza vaccine (Q/LAIV) developed by MedImmune. Q/LAIV contains both of the influenza B virus lineages, in contrast to available trivalent vaccines that include only one of the two lineages that co-circulate each year. This trial compared the safety and immunogenicity of Q/LAIV with that of two trivalent LAIVs (T/LAIVs) in children from 2 years to 17 years of age.

Children were randomized 3:1:1 to receive Q/LAIV or one of two T/LAIV vaccines. Subjects aged 9 years to 17 years received one dose, and those aged 2 years to 8 years received two doses one month apart. Serum immune responses, measured as geometric mean titers (GMTs) of hemagglutination inhibition antibodies, were evaluated one month after the single dose or two-dose series.

Q/LAIV was found to be noninferior to T/LAIV: the upper bounds for all four 95% confidence intervals for the post-dose GMT ratios (T/LAIV divided by Q/LAIV) were ≤1.5, the predefined noninferiority margin. The overall seroresponse rates were also comparable between treatment groups. Adverse event rates for the three treatment groups were comparable excepting fever, which was more common after dose 1 in Q/LAIV subjects (5.1%) than in T/LAIV subjects (3.1%) between 2 years and 8 years of age.