Cross-clade immunogenicity and safety of an AS03A-adjuvanted prepandemic H5N1 influenza vaccine in Hong Kong

To present Hong Kong'Äìspecific data from a large Asian population (also involving Thailand, Singapore, and Taiwan) on safety and manufacturing consistency across four AS03(A)-adjuvanted H5N1 vaccine formulations in terms of immune response against the A/Vietnam/1194/2004 strain. Immunogenicity against the heterologous A/Indonesia/05/2005 strain was also assessed. NCT Number: 00449670. Prospective, observer-blind study. Out-patient clinic of a tertiary hospital in Hong Kong. A total of 360 subjects aged 18 to 60 years were randomised into six groups to receive two doses (21 days apart) of the study vaccine. One of the four adjuvanted formulations (3.75 microgram H5N1 haemagglutinin [HA]+AS03(A)) of the vaccine (H5N1-AS03(A)) or one of the two non-adjuvanted (3.75 microgram H5N1 [HA]) formulations of the vaccine (H5N1-DIL). Blood samples collected before vaccination and 21 days after each vaccine dose were analysed using haemagglutination-inhibition and neutralisation assays. Solicited, unsolicited, and serious adverse events were recorded. Manufacturing consistency across all four vaccine formulations was demonstrated. After two doses, the AS03(A)-adjuvanted prepandemic influenza vaccine demonstrated high seroprotection rates against the A/Vietnam/1194/2004 strain (95.8%) and good immunogenicity against the heterologous A/Indonesia/05/2005 strain (45.7%), as compared to the non-adjuvanted vaccine (4.6% and 1.5%, respectively). The seroconversion rates induced by the adjuvanted formulations in terms of viral neutralising antibodies against the two strains were much higher than those induced by the non-adjuvanted formulations. There were no safety concerns for any of the adjuvanted vaccine formulations. The AS03(A)-adjuvanted H5N1 prepandemic influenza vaccine demonstrated good immunogenicity and an acceptable safety profile in Hong Kong.