Serum specimens collected in 1966 from individuals of different age groups were studied for the presence of haemagglutination inhibition (HI) antibody to four influenza viruses. All sera were from individuals of blood group A or O and in no instance was the incidence of antibody to a virus strain significantly greater for persons of blood group O compared with similar aged individuals of blood group A. This finding for HI antibody to A 2/Singapore/1/57 is different from similar studies of serum specimens collected in 1961–3. It is suggested that the change in the immune status of a population, with reference to blood-group status, is due to repeated exposure to infection; this changing pattern of immune status is discussed.
Similar studies of HI antibody to adenovirus type 3 and 7 in human sera from persons of blood group A and O shows a changing pattern with increasing age. These results are consistent with the findings for influenza virus and are discussed. Repeated exposure of a population to infection results in obscuring genetically determined variations in susceptibility.
I would like to thank Professor M. G. McEntegart, Professor of Medical Microbiology, and Professor C. H. Stuart-Harris, Professor of Medicine, for their advice and criticism, and Miss D. Coles, F.I.M.L.T., and Mrs P. Robinson for expert technical assistance.