Stability testing in Haemophilus influenzae type b conjugate vaccines

Coupling T-cell-independent antigens such as the capsular-polysaccharide (PRP) of H. influenzae type b (HIB) to a T-cell-dependent protein-carrier enhances the immune response, particularly in individuals who are poor responders to such antigens. An adequate immunogenicity is dependent upon the characteristics of the PRP antigen, the protein carrier, the efficiency of conjugation and the stability of the conjugate. Since adequate immunogenicity tests are not available, stability studies in such products are essentially confined to molecular size distribution and determination of the degree of conjugation. A better understanding of the factors involved in stability and an improvement of the testing methods are highly desirable.