Evaluation of trivalent, live, cold-adapted (CAIV-T) and inactivated (TIV) influenza vaccines in prevention of virus infection and illness following challenge of adults with wild-type influenza A (H1N1), A (H3N2), and B viruses

Abstract

Trivalent, live, cold-adapted influenza vaccine (CAIV-T) is highly effective in the prevention of influenza in children, and a variety of monovalent and bivalent cold-adapted influenza vaccines have been efficacious in adults. In order to determine the efficacy of CAIV-T in healthy adults, we administered CAIV-T, trivalent inactivated influenza vaccine (TIV) or placebo to 103 adults in randomized double-blind fashion, and then challenged those subjects who had pre-screening serum hemagglutination-inhibition antibody titers of 1:8 or less with wild-type influenza viruses corresponding to the strains contained in the vaccine. CAIV-T was well tolerated. Upon challenge with wild-type influenza virus, laboratory documented influenza illness (respiratory symptoms with either isolation of wild-type influenza virus from nasal secretions or 4-fold and/or greater HAI antibody response to challenge) occurred in 14/31 (45%) placebo recipients, 4/32 (13%) TIV recipients, and 2/29 (7%) CAIV-T recipients. The estimated protective efficacy of CAIV-T was therefore 85% and of TIV was 71%. These results are consistent with those of previous studies using monovalent preparations of cold-adapted influenza vaccine in this model, and indicate that CAIV-T will be an effective means to prevent influenza illness in adults.