Safety and antigenicity of non-adjuvanted and MF59-adjuvanted influenza A/Duck/Singapore/97 (H5N3) vaccine: a randomised trial of two potential vaccines against H5N1 influenza

Background In 1997, pathogenic avian influenza A/Hong Kong/97 (H5N1) viruse s emerged as a pandemic threat tc human beings, A non-pathogenic variant, i nfluenza A/Duck/Singapore/97 (H5N3), was identified as a leading vaccine ca ndidate. We did an observer-blind, phase I, randomised trial in healthy vol unteers to assess safety, tolerability, and antigenicity of MF59-adjuvanted and non-adjuvanted vaccines. Methods 32 participants were randomly assigned MF59, and 33 non-adjuvanted vaccine. Two doses were given 3 weeks apart, of 7.5, 15, or 30 mug haemaggl utinin surface-antigen influenza A H5N3 vaccine. Antibody responses were me asured by haemagglutination inhibition, microneutralisation, and single rad ial haemolysis (SRH). The primary outcome was geometric mean antibody titre 21 days after vaccination. Findings The A/Duck/Singapore vaccines were safe and well tolerated. Antibo dy response to non-adjuvanted vaccine was poor, the best response occurring after two 30 mug doses: one, four, four, and one person of eleven seroconv erted by haemagglutination inhibition, microneutralisation, H5N3 SRH, and H 5N1 SRH, respectively. The geometric mean titres of antibody, and seroconve rsion rates, were significantly higher after MF59 adjuvanted vaccine. Two 7 .5 mug doses of MF59 adjuvanted vaccine gave the highest seroconversion rat es: haemagglutination inhibition, six of ten; microneutralisation, eight of ten; H5N3 SRH, ten of ten; H5N1 SRH, nine of ten. Geometric mean titre of antibody to the pathogenic virus, A/Hong Kong/489/97 (H5N1), was about half that to A/Duck/Singapore virus. Interpretation Non-adjuvanted A/Duck/Singapore/97 (H5N3) vaccines are poorl y immunogenic and doses of 7.5-30 mug haemagglutinin alone are unlikely to give protection from A/Hong Kong/97 (H5N1) virus. Addition of MF59 to A/Duc k/Singapore/97 vaccines boost the antibody response to protection levels. O ur findings have implications for development and assessment of vaccines fo r future pandemics.