Immunogenicity assays and surrogate markers to predict vaccine efficacy.

Immunogenicity of vaccines is most often evaluated by measuring the antibody concentration before and after vaccination. The assessment of cellular responses is far more laborious and difficult to standardize. However, the antibody concentration is not the sole criterion because different vaccine formulations can induce antibodies of different fine specificity and functional activity. The quality of antibodies can be measured in several ways; e.g. the information on isotype distribution, avidity and bactericidal, opsonizing and neutralizing capacity can be useful. As an example, the use of these surrogate assays for evaluation of Haemophilus influenzae type b (Hib) conjugate vaccines is described. The same assays can most probably be used to assess the potency of other conjugate vaccines that are now in phase I-III trials.