Postvaccination increase in serotype 19A pneumococcal disease in Norway is driven by expansion of penicillin-susceptible strains of the ST199 complex.

Serotype replacement in invasive pneumococcal disease has been observed after widespread use of the 7-valent pneumococcal conjugate vaccine (PCV7). Replacement is dominated by penicillin-nonsusceptible serotype 19A in several countries. Antibiotic selection pressure has been proposed to interact with immunization, leading to rapid replacement. In Norway, where prescription of antibiotics is limited, post-PCV7 replacement by serotype 19A is dominated by penicillin-susceptible clones. Hence, serotype 19A replacement occurs, although it is not driven by antibiotic selection pressure.