PILOT TRIAL OF A PENTAVALENT PNEUMOCOCCAL POLYSACCHARIDE PROTEIN CONJUGATE VACCINE IN GAMBIAN INFANTS/

Background. Invasive pneumococcal disease is a major cause of mortalit y and morbidity in young children in developing countries. Pneumococca l polysaccharide/protein conjugate vaccines, which are likely to be im munogenic in the very young, offer a potential way for preventing thes e infections. Therefore a pilot safety and immunogenicity study of a f ive-valent conjugate vaccine has been undertaken in an area of rural A frica where invasive pneumococcal disease is prevalent. Methods. Thirt y Gambian infants were vaccinated with 3 doses of a five-valent pneumo coccal conjugate vaccine containing 5 mu g of type 6B, 14, 18, 19F and 23F polysaccharides conjugated to the diphtheria toxin mutant protein CRM(197) at the ages of 2, 3 and 4 months; 30 infants received 2 dose s at the ages of 2 and 4 months and 30 infants who received three dose s of a Haemophilus influenzae type b vaccine acted as controls. Local and systemic reactions were recorded after vaccination and antibody ti ters were measured by an enzyme-linked immunosorbent assay. Results. N o serious local or systemic reactions to vaccination were recorded. An tibody responses to each component of the vaccine were demonstrated. O ne month after immunization with three doses of vaccine, antibody tite rs were 3 to 11 times higher than before vaccination (postvaccination titers ranged from 2.49 mu g/ml for type 19 polysaccharide to 7.59 mu g/ml for type 14). Elevated titers were well-maintained during the sub sequent 4 months. Three doses of vaccine induced higher titers than di d two doses. Antibody titers increased 2- to 3-fold over the period of immunization in children who received H. influenzae type b vaccine. C onclusions. A five-valent pneumococcal conjugate vaccine proved safe a nd immunogenic in Gambian infants. However. a vaccine containing a lar ger number of serotypes will be necessary to achieve a maximal clinica l impact.