A novel enzyme-linked immuno-sorbent assay (ELISA) for the quantification of total and free polysaccharide in Haemophilus influenzae b-Tetanus toxoid conjugate vaccines in monovalent and combined vaccine formulations.

Current Haemophilus influenzae b conjugate vaccines (Hib), which are made of purified capsular polysaccharide (poly-ribosyl-ribitol-phosphate; PRP) conjugated to a carrier protein, are almost completely evaluated by physico-chemical methods to ensure the integrity and stability of the vaccine and consistency of manufacture of batches. The absence of a potency assay makes the quantification of total PRP content (in SI units) and of % free polysaccharide in final fills or bulk components of Hib vaccines critical release tests for both manufacturers and national control authorities. Here we describe a simple and sensitive Enzyme-Linked Immuno-sorbent Assay (ELISA) which has been developed to quantify total and free PRP content in Hib-TT vaccine alone or when in combination with other vaccines. The assay is robust, specific and highly sensitive.