Determination of antibody responses of elderly adults to all 23 capsular polysaccharides after pneumococcal vaccination

The 23-valent pneumococcal polysaccharide vaccine was formulated to prevent invasive infection in the elderly and other high-risk populations from the most prevalent Streptococcus pneumoniae serotypes. However, the immunogeni city of all 23 vaccine polysaccharides has not been fully characterized in elderly adults, We previously reported that whereas the majority of elderly subjects had vigorous immune responses to selected pneumococcal vaccine po lysaccharides, a subset of elderly individuals responded to fewer than two of seven vaccine serotypes after immunization. To determine whether these e lderly low responders have a general inability to respond to pneumococcal v accine and to determine whether elderly low responders might be identified by their responses to a few polysaccharides, we measured antibody responses of elderly adults to all 23 vaccine polysaccharides after pneumococcal imm unization. As a group, elderly subjects showed a significant rise after imm unization in geometric mean antibody levels to all 23 vaccine serotypes. Ho wever, when individual rather than group immune responses were assessed, th e 23-valent vaccine did not appear to be uniformly immunogenic in these eld erly subjects. Eleven elderly subjects (20%) had twofold increases in speci fic antibody after vaccination to only 5 or fewer of the 23 vaccine polysac charides, and they did not respond to the most prevalent serotypes causing invasive disease. Antibody responses to serotype 9N were found to reliably distinguish low vaccine responders from other elderly subjects. However, no particular group of vaccine polysaccharides could be used as a marker for adequate immune responses if only postvaccination sera were analyzed.