ackground. Effective planning and preparedness against a possi- ble future A/H5N1 influenza pandemic is a major global challenge. Because dose sparing strategies are required to meet the global demand for vaccine, efforts have focused on the development of adju- vanted vaccine formulations of relatively lower antigen content. Aim. This study aimed to demonstrate the non-inferiority of a low-antigen-dose (3.75 mg) A/H5N1 pre-pandemic vaccine com- pared with a licensed, higher-dose (7.5 mg) formulation in adult and elderly subjects. Immunogenicity was assessed according to European and U.S. licensure criteria.
Methods. A total of 722 subjects were randomized in equal num- bers to receive either the licensed or low-dose formulation. All subjects received two vaccine doses administered three weeks apart. Immunogenicity was assessed three weeks after the admin- istration of each vaccine dose by hemagglutination inhibition HI), single radial haemolysis (SRH) and microneutralization assays (MN). Local and systemic reactions were assessed over a seven day period post-vaccination. Adverse events were recorded throughout.
Results. The low-dose vaccine was demonstrated to be non-infe- rior to the licensed formulation in terms of antibody titres against the vaccine strain. All three European licensure criteria were met by adult subjects in response to the low-dose vaccine; two crite- ria were met by the elderly age group. Cross-reactive antibodies were detected against the heterologous A/H5N1 antigen strains A/Indonesia/05/05 and A/turkeyTurkey/01/05. Both vaccines were generally well tolerated by both age groups.
Conclusion. These data demonstrate that a low antigen dose in combination with MF59Â® adjuvant is adequate for the routine pre-pandemic immunization of adult and elderly subjects.