Vaccines with acceptable efficacy profile against the H1N1 A/California/7/2009 virus are needed for use in children. The two studies presented here evaluated the immunogenicity and the reactogenicity/safety of A/H1N1/2009 vaccines containing either 3.75 μg haemagglutinin antigen (HA) and AS03(A)-adjuvant (3.75 μg HA/AS03(A) study) (N=210 [53, 57 and 100 in the 3-5, 6-9 and 10-17 years age strata, respectively]) or 1.9 μg HA and AS03(B)-adjuvant (1.9 μg HA/AS03(B) study) (N=244 [61, 65 and 118 in the 3-5, 6-9 and 10-17 years age strata, respectively]), given as two-dose series. Although the haemagglutination inhibition antibody titres were higher in the 3.75 μg HA/AS03(A) study, both vaccine dosages were highly immunogenic and exceeded regulatory acceptance criteria after the first and the second doses. Seroprotection rates reached 100% and seroconversion rates ranged from 98.2% to 99.1% after each dose of both vaccine dosages. Geometric mean titres increased from 456.5 to 1538.5 and from 297.9 to 1106.7 between the first and the second doses in the 3.75 μg HA/AS03(A) study and the 1.9 μg HA/AS03(B) study, respectively. Despite an observed slight increase of the reactogenicity following the second dose in the 3.75 μg HA/AS03(A) study, the vaccines safety profiles were considered clinically acceptable. In conclusion, both dosages of the AS03-adjuvanted A/H1N1/2009 pandemic influenza vaccines were highly immunogenic and well-tolerated in children and adolescents.
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