Epidemiological, immunological and virulence characteristics of persistent Streptococcus pneumoniae vaccine serotypes following vaccine introduction.

Streptococcus pneumoniae vaccine serotypes can persist despite pneumococcal conjugate vaccine (PCV) introduction. To examine serotype persistence, we leverage 6,545 nasopharyngeal swabs collected from children hospitalised with pneumonia before and after PCV13 introduction in Mongolia. DNA microarray was used to identify changes in lineage composition within serotypes 6A, 6B, 14, 19F and 23F over the six-year surveillance period. Children carrying post-PCV lineages are less likely to have severe pneumonia (serotypes 6B, 14 and 19F) and be multi-drug resistant (serotypes 6A, 6B and 23F) than pre-PCV lineages. Of note, the post-PCV lineage of serotype 6B has lower antibody binding to capsule and expression of capsule genes, thinner capsule and is less virulent in mice compared with the pre-PCV lineage. Our data show that although vaccine serotypes can persist in vaccinated populations, vaccination may select for less virulent lineages within vaccine serotypes. Therefore, considering factors beyond serotype is important when evaluating the true value of vaccination.