Pneumococcal infections (pneumonia, otitis media, sinusitis, meningitis) are common and usually involve toddlers and the elderly. Currently, two pneumococcal vaccines are in clinical use. The older vaccine consists of pure capsular polysaccharides from 23 pneumococcal serotypes and induces only a limited B-cell response because polysaccharides are poor antigens that stimulate mainly B-cells. In 2000, a vaccination program with a novel 7-valent pneumococcal conjugate vaccine was launched in the U.S. The conjugation of capsular polysaccharides with a highly immunogenic diphtheria toxoid protein induces both a T cell and B cell response that results in specific humoral and mucosal immunity. Since children are the main reservoir of pneumococci, the 7-valent conjugate vaccine seems to eradicate the respective pneumococcal serotypes within the population, as demonstrated by recent US data. Pronounced herd immunity resulted in a decrease in invasive pneumococcal diseases in vaccinees and non-vaccinees as well as in a reduction of antibiotic resistance rates. However, recent data suggest a replacement of vaccine-serotypes by non-vaccine serotypes, which conquer the ecological niche created by the vaccine. In order to encounter this problem a 13-valent conjugated vaccine is currently under development.