RESUMEN
BACKGROUND: Effective planning and preparedness against a possible 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 adjuvanted vaccine formulations of relatively lower antigen content. AIM: This study aimed to demonstrate the non-inferiority of a low-antigen-dose (3.75 µ) [DOSAGE ERROR CORRECTED] A/H5N1 pre-pandemic vaccine compared 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 numbers 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 administration 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-inferior 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 criteria 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 MF59 adjuvant is adequate for the routine pre-pandemic immunization of adult and elderly subjects.