Reduced levels of clinical or radiological pneumonia in clin- ical trials of a nine-valent pneumococcal conjugate vaccine provide an estimate of the vaccine-preventable disease burden (valency indicates the number of serotypes against which the vaccine provides protection; conjugate refers to conjugation of polysaccharides to a protein backbone). In a study in The Gambia, 37 percent of radiological pneumonia was prevented, reflecting the amount of disease caused by S. pneumoniae, and mortality was reduced by 16 percent (Cutts and others 2005). Upper respiratory tract colonization with potentially patho- genic organisms and aspiration of the contaminated secretions have been implicated in the pathogenesis of bacterial pneumo- nia in young children. Infection of the upper.
