A Phase II Study of an Investigational Tetravalent Influenza Vaccine Formulation Combining MF59®: Adjuvanted, Pre-pandemic, A/H5N1 Vaccine and Trivalent Seasonal Influenza Vaccine in Healthy Adults

An investigational tetravalent vaccine combining pre-pandemic, MF59®-adjuvanted A/H5N1 vaccine with non-adjuvanted, trivalent, seasonal influenza vaccine has been developed, which has the potential to be used for pre-pandemic priming and to improve levels of compliance and coverage. It is important to determine whether the safety and immunogenicity of the combination vaccine is equivalent to that of the two separate vaccines when administered concomitantly. Healthy adults (n=601) were randomly assigned to three vaccination groups to receive either: (1) tetravalent vaccine and placebo concomitantly (in separate arms) on Day 1, followed by A/H5N1 vaccine on Day 22; (2) A/H5N1 vaccine and placebo concomitantly on Day 1, followed by tetravalent vaccine on Day 22; or (3) A/H5N1 and seasonal vaccines concomitantly on Day 1, followed by A/H5N1 vaccine on Day 22. Antibody responses were measured using single radial hemolysis (SRH), haemagglutination inhibition (HI), and microneutralization (MN) assays on Days 1, 22, and 43. Solicited adverse reactions were recorded for seven days after vaccination. Spontaneous adverse events were recorded throughout the study. The tetravalent vaccine elicited antibody titers equivalent to those for separate A/H5N1 and seasonal vaccines, and sufficient to meet the European licensure criteria against A/H5N1 and all three seasonal strains. Local and systemic reactions were mainly mild to moderate. No vaccine-related serious adverse events occurred. These findings demonstrate that MF59-adjuvanted A/H5N1 and seasonal influenza vaccines had an acceptable safety profile and could be effectively administered as a tetravalent formulation, supporting the possibility of integrating pre-pandemic priming into seasonal influenza vaccination programs.