Rapid Licensure of a New, Inactivated Influenza Vaccine in the United States

Background: The unexpected problems at 1 of 2 US licensed manufacturers of trivalent inactivated influenza virus vaccine (TIV) in 2004 highlights the urgent need for additional vaccine sources. We evaluated a split virus TIV (Fluarix, GSK), to generate data supportive of a license application in the US. Methods: Healthy adults ages 18-64 years at four centers were randomly assigned to receive a single IM injection of Fluarix (n = 763) or placebo (n = 193) in double-blind fashion. Subjects were monitored for safety and serum hemagglutination-inhibition (HAI) titers determined before and 21 days after vaccination. Results: Vaccine was well tolerated, with only mild to moderate myalgias and injection site pain and redness being more common in vaccine than placebo recipients. Four-fold or greater increases in serum HAI titers were seen in 60%, 62% and 78% of vaccine recipients against the H1, H3, and B components of the vaccine, respectively, and post-vaccination titers of > 1:40 achieved in 98%, 99% and 99% of subjects, exceeding the prespecified criteria for acceptability for all three antigens. Conclusions: Fluarix has a safety and immunogenicity profile like other US-licensed inactivated influenza vaccines and should be effective when used to immunize US adults. Summary Line: the results of this study were pivotal for the rapid approval of Fluarix in the US for use in adults 18 years of age or older.