Provision of data useful for the development of a conjugate pneumococcal vaccine is the subject of two studies published in this issue of JAMA. Both Eskola et al1 and the Israeli Pediatric Bacteremia and Meningitis Group2 looked at the epidemiology of pneumococcal infections in children to discover the extent of disease, prevalent serotypes, and definition of a high-risk target population of children as preliminary steps in devising a conjugate pneumococcal vaccine strategy. Why is the current vaccine, which has worked well in adults, not used for children, and why go to the trouble of developing a conjugate vaccine?
It has been known for decades that the capsular polysaccharides of Streptococcus pneumoniae confer the antigenic specificity that defines different serotypes and that antibodies to these polysaccharides (also known as soluble-specific substances) are type-specific and protective for human beings. In 1945, MacLeod and associates3 showed that these polysaccharides, used