RESUMEN
BACKGROUND: Avian influenza A H9N2 strains have pandemic potential. METHODS: In this randomized, observer-blind study (ClinicalTrials.gov: NCT01659086), 420 healthy adults, 18-64years of age, received 1 of 10 H9N2 inactivated split-virus vaccination regimens (30 participants per group), or saline placebo (120 participants). H9N2 groups received 2 doses (days 0, 21) of 15µg hemagglutinin (HA) without adjuvant, or 1.9µgHA+AS03A, 1.9µgHA+AS03B, 3.75µgHA+AS03A, or 3.75µgHA+AS03B; followed by the same H9N2 formulation or placebo (day 182). AS03 is an adjuvant system containing α-tocopherol (AS03A: 11.86mg; AS03B: 5.93mg) and squalene in an oil-in-water emulsion. Immunogenicity (hemagglutination inhibition [HI] and microneutralization assays) and safety were assessed up to day 546. RESULTS: All adjuvanted formulations exceeded regulatory immunogenicity criteria at days 21 and 42 (HI assay), with seroprotection and seroconversion rates of ≥94.9% and ≥89.8% at day 21, and 100% and ≥98.1% at day 42. Immunogenicity criteria were also met for unadjuvanted vaccine, with lower geometric mean titers. In groups administered a third vaccine dose (day 182), an anamnestic immune response was elicited with robust increases in HI and microneutralization titers. Injection site pain was reported more frequently with adjuvanted vaccines. No vaccine-related serious adverse events were observed. CONCLUSIONS: All H9N2 vaccine formulations were immunogenic with a clinically acceptable safety profile; adjuvanted formulations were 4-8 times dose-sparing (3.75-1.9vs 15µgHA). TRIAL REGISTRATION: Registered on ClinicalTrials.gov: NCT01659086.