Pneumococcal infection and immunization in children.

Pneumococcal infection persists as a major cause of pneumonia, bacteremia, and otitis media and is the important cause of meningitis in young children. Children less than 2 years of age show the highest incidence of pneumococcal diseases. Pneumococcal types 6A + 6B, 7F, 9V, 14, 18C, 19F + 19A, and 23F account for the large majority of disease isolates in the pediatric population. Bacterial clearance and antibody response were studied in young mice from mothers injected with pneumococcal type 9V polysaccharide (PS) conjugated with the inactivated pneumolysin to examine the protective immunity of young mice to pneumococcal infection. The injection of mice with pneumococcal PS-protein conjugate conferred the protective immunity to pneumococcal infection. The efficacy of pneumococcal vaccine might be enhanced by addition of inactivated pneumolysin in the form of PS-protein conjugate. The molecular size of pneumococcal type 19F PS or oligosaccharide used for preparing the PS-protein conjugate has a profound effect on the antibody response to the PS. The conjugate immunogen prepared from a large molecule of 19F PS produced a high antibody response to the PS in young mice. Development of a PS-protein conjugate vaccine for selected pneumococcal types will help in solving problems of poor immunogenicity of pneumococcal PS vaccine in young children.