STREPTOCOCCUS PNEUMONIA CAPSULAR POLYSACCHARIDE-DIPHTHERIA TOXOID CONJUGATE VACCINE IS IMMUNOGENIC IN EARLY INFANCY AND ABLE TO INDUCE IMMUNOLOGICAL MEMORY

Background. Pneumococcal polysaccharide vaccines are not protective ag ainst the most common pneumococcal infections in infancy. The importan ce of pneumococcal diseases and emerging antimicrobial resistance emph asize the need for prophylaxis. Methods. Pneumococcal conjugate vaccin e, containing capsular polysaccharides from serotypes 6B, 14, 19F and 23F conjugated to diphtheria toroid (PncD), was given to 75 infants at 2, 4 and 6 months of age. Three dosages (1, 3 or 10 mu g of each) wer e used. A placebo group of 49 infants received physiologic saline. Chi ldren were given a booster dose of either polysaccharide or conjugate vaccine at 14 months of age; the placebo group received conjugate vacc ine. Antibody concentrations were determined with an enzyme immunoassa y. Results. The highest dose induced the strongest response after prim ary immunization, but booster response was greatest in the group prime d with the lowest dose. Polysaccharide and conjugate vaccines induced booster responses of the same magnitude. At 24 and 36 months of age th e antibody concentrations were similar in children who had received th e PncD in infancy and in children immunized at 14 months of age only. Conclusions. The PncD conjugate vaccine is immunogenic and able to ind uce immunologic memory.