Background: Alternative methods for influenza vaccine production are needed to ensure adequate supplies.
Methods: Healthy adults 50-64 years were assigned randomly to receive one intramuscular injection of trivalent recombinant hemagglutinin (rHA) or U.S. licensed trivalent inactivated vaccine (TIV) containing H1, H3 and B antigens (Ag) derived from 2007 to 2008 influenza virus strains A/Solomon Islands/03/2006 (H1N1), A/Wisconsin/67/2005 (H3N2), and B/Malaysia/2506/2004. Each rHA dose contained 45 μg HA/strain of the 2007-2008 FDA-recommended Ag vs. 15 μg/strain for TIV. Antibody (Ab) responses were measured using a hemagglutination-inhibition (HAI) assay at baseline and 28 days post-vaccination. Respiratory samples for viral culture were collected from subjects with influenza-like illness (ILI) during the 2007-2008 season in the U.S.
Results: 601 subjects were enrolled. Vaccines were well tolerated. Seroconversion (the percentage of subjects with either (a) a pre-vaccination HAI titer ≤ 10 and a post-vaccination HAI titer ≥ 40 or (b) a pre-vaccination titer ≥ 10 and a minimum four-fold rise in post-vaccination HAI antibody titer) in the TIV and rHA groups, respectively, was obtained in 66% vs. 72% for H1; 44% vs. 61% for H3; and 41% vs. 41% for B. Proportions achieving titers ≥ 40 were 96% vs. 96% for H1, 75% vs. 85% for H3, and 94% vs. 93% vs. B. Geometric mean titer ratios at day 28 (TIV/rHA) were 0.77 for H1; 0.58 for H3; and 1.05 for B, respectively. ILI frequencies were low and similar in both groups.
Conclusions: Both vaccines were safe and immunogenic. Ab responses vs. H1 and H3 Ags were significantly higher in the rHA group, with similar responses to B. Furthermore, the FluBlok group had a statistically significantly higher seroconversion rate against influenza A/H3N2 compared to the TIV group.
Trial registration: ClinicalTrials.gov NCT00539864.
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