Impact of conjugate pneumococcal vaccines on antibiotic resistance.

Reduction of drug-resistant Streptococcus pneumoniae (DRSP) by pneumococcal conjugate vaccines (PCVs) has recently become a reality. We now know that (1) most clinically significant DRSP strains belong to seven serotypes (6A, 6B, 9V, 14, 19A, 19F, 23F), (2) five (6B, 9V, 14, 19F, 23F) of the seven are constituents of heptavalent PCV (PCV7), and (3) the remaining two serotypes (6A, 19A) are immunologically related to serotypes in PCV7, but only 6A has been reduced by PCV7. Furthermore, PCVs can also reduce DRSP in unvaccinated individuals (herd immunity). PCVs lead to a reduction in antibiotic use, which is also potentially helpful to contain DRSP. Although a reduction in disease caused by most penicillin-resistant strains has been reported, reductions in intermediately penicillin-resistant strains has not been shown to the same degree, because of increased intermediate resistance among non-PCV7 serotypes. Serotype 19A, which is both antibiotic resistant and a common cause of disease, is not affected by PCV7, and is now increasing worldwide, including in countries without PCV7. Continued exposure of non-PCV7 serotypes to antibiotic pressure may reduce the overall impact of PCVs on DRSP. Further strategies include expansion of PCV serotype coverage, development of protein-based vaccines, and further limitation of antibiotic use.