IMMUNOGENICITY OF STANDARD AND LOW-DOSE VACCINATION USING YEAST-DERIVED RECOMBINANT HEPATITIS-B SURFACE-ANTIGEN IN ELDERLY VOLUNTEERS

There is no conclusive evidence that age influences the response to vaccination against hepatitis B virus. We therefore studied the immunogenicity of yeast-derived rHBsAg vaccine in elderly volunteers. The study was conducted in the outpatient clinics of an academic and a regional hospital, in a rural family practice and in an urban community centre. We recruited 112 healthy volunteers aged 59 years and over, to whom 10 or 20 mu g yeast-derived HBsAg was given at 0, 1 and 6 months. Anti-HBs titres were measured by radioimmunoassay at 2, 6 and 7 months. Responders and non-responders were compared using univariate non-parametric tests and multivariate logistic regression analysis. Of the 116 subjects who volunteered to take part in the study, 106 vaccinees completed it. The percentage of subjects with an anti-HBs titre greater than or equal to 10 IUl(-1) at 7 months was 60% (95% confidence interval: 51-70%; geometric mean titre: 253 IUl(-1)). Of the factors studied, i.e. setting, age, sex, alcohol consumption, current medication and vaccine dose, the use of medication at the time of the first vaccination was the only independent factor related to the response to vaccination, with a response rate of 78% (95% confidence interval. 66-89%) in those without medication. In elderly subjects, the proportion with protective concentrations of anti-HBs after vaccination with 10 or 20 mu g yeast-derived recombinant HBsAg in a standard scheme is lower than in healthy adolescents. Within the older age group studied here, the use of medication, probably reflecting general health, is the only significant factor influencing the response to vaccination.