Abstract
The effect of blood group status on the incidence of epidemic influenza A (H3N2) infections and on serological response to influenza vaccination with killed subunit and live attenuated vaccines have been investigated during comparative vaccine trials in Western Australia. A significantly higher incidence of epidemic influenza was observed in subjects of blood group B compared with those of other blood groups, regardless of whether they had serological evidence of previous exposure to H3N2 antigens or not. Volunteers of different blood groups exhibited similar seroconversion frequencies to both vaccines after the administration of two doses, but a significantly higher proportion of blood group A subjects seroconverted after receiving their first dose of live attenuated vaccine compared with those of other blood groups. Although this finding was inconsistent with the increased incidence of epidemic influenza in subjects of blood group B, it is discussed in terms of the methods employed to obtain attenuation. Higher geometric mean HI antibody titres were observed in blood group O subjects after the administration of killed subunit vaccine. The results described in this report supported the contention that genetic factors linked to ABO blood groups may play a role in susceptibility to infection with influenza A virus, but that any association must be indirect.