The state of pneumococci asymptomatic carrier in children and its relation to the invasive disease. What has changed after the conjugated vaccine introduction?

Some important changes relating to the pneumococcal invasive disease (PID) have happened in the last decade in developed countries. The effectiveness of the pneumococcal conjugate heptavalent vaccine (PCV-7) in diminishing the PID by the serotypes included (STV) has been proved after its generalization, but some new serotypes not included have aroused with force as cause of PID. Fortunately, the load of the disease by not included serotypes in children younger than five years is much lower than the caused by STV before the vaccine, and this tendency seems steady with time. But this process has followed parallel to similar changes in the nasopharyngeal colonization by pneumococci, very frequent in under five children, so that now STV have dramatically diminished in healthy carriers and have been substituted by non vaccine serotypes that end by causing PID. This serotypes’ replacement have made the antibiotic resistances to diminish due to the fact that they were more prevalent among STV. Two new conjugated vaccines have been commercialized recently and they extend the protection to new serotypes. This paper reviews the changes, expectations and uncertainties that open this new stage in conjugated penumococcal vaccines.