Since their widespread usage, both invasive and non-invasive pneumococcal diseases and nasopharyngeal carriage of streptococcus pneumoniae(Spn) have demonstrated their effectiveness . For this degree of safety, the immunisation regime in the United States was a three-dose regimen with one booster (3 + 1). Alternatively, in several countries the WHO-approved 3 + 0 or 2 + 1 schedules for reducing vaccine costs are being implemented. Sustained pneumococcal disease and carriage defence includes persistent antibody and cellular immune memory levels.

Antibody responses to PCVs have been thoroughly studied, but the cellular response to the vaccine in young children is not well known. To assess improvements in the adaptive immune response, researchers examined circulating PCV-13 serotype-specific B and T cell memory in paired blood samples from children before and after PCV13 dose 3 and booster immunizations. There were no major variations in memory B cell populations between post dose 2 and post dose 3. However, as compared to the pre-booster, the booster dose substantially increased the frequency of Spn-specific memory B cells. The method used did not detect Spn-specific memory T cells.

These results indicate that booster vaccinations can affect long-term antibody protection titers by increasing spn-specific memory B cells.