Pneumococcal capsular polysaccharide immunity in the elderly.

Immunity against pneumococcal infections is impaired in older people, and current vaccines are poorly protective against pneumococcal disease in this population. Naturally-acquired immunity against pneumococcal capsular polysaccharides develops during childhood and is robust in young adults, but deteriorates with advanced age. In particular, antibody levels and function are reduced in older people. Pneumococcal vaccines are recommended for people over 65 years of age. However, the benefits of polysaccharide and protein-conjugated vaccines in this population are small, due to both serotype replacement and incomplete protection against vaccine-serotype pneumococcal disease. In this review we overview the immune mechanisms by which naturally-acquired and vaccine-induced pneumococcal capsular polysaccharide immunity declines with age, including altered colonization dynamics, reduced opsonic activity of antibodies (particularly IgM) and impaired mucosal immunity.