Evaluation of the safety, reactogenicity and immunogenicity of FluBlok® trivalent recombinant baculovirus-expressed hemagglutinin influenza vaccine administered intramuscularly to healthy adults 50-64 years of age

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 (HI NI), A/Wisconsin/67/2005 (H3N2), and B/Malaysia/2506/2004. Each rHA dose contained 45 mu g HA/strain of the 2007-2008 FDA-recommended Ag vs. 15 mu g/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. (C) 2011 Elsevier Ltd. All rights reserved.