Epidemiology of Streptococcus pneumoniae serotypes in children before and after pneumococcal vaccination

Aim. To investigate how the pneumococcal vaccination affects the distribution of Streptococcus pneumoniae serotypes.Materials and Methods. In 2011-2019, 1,852 healthy children (1,354 aged ≤ 5 years and 480 aged from 6 to 17 years) were examined for the nasopharyngeal pneumococcal carriage. Of them, 539 children were tested before the start of pneumococcal vaccination (2011-2014), while 1,313 were tested during the vaccine campaign (2015-2019). Pneumococcal strains were serotyped using multiplex polymerase chain reaction.Results. Streptococcus pneumoniae serotype distribution considerably differed between children ≤ 5 and 6-17 years of age. Serotypes 23F, 19F, 19A, 6AB, and 15BC were prevalent in children ≤ 5 years of age while the older children were characterised by a high prevalence of capsular serotypes (3 and 33AF/37), serogroup 9 (9AV and 9LN), non-typeable streptococci, as well as 19F, 6AB and 6CD serotypes. Vaccination was associated with a significantly decreased prevalence of Streptococcus pneumoniae carriage (from 41.5% to 19.2%) among children ≤ 5 years of age, while this reduction was less pronounced (from 13.5 to 9.0%) in older children. Vaccination led to the shift in the distribution of pneumococcal serotypes towards an increased prevalence of non-vaccine serotypes that was particularly prominent in children ≤ 5 years of age. In particular, vaccination reduced the prevalence of 23F and 19A pneumococcal serotypes but heightened prevalence of 11AD serotype and to the appearance of previously undetected serotypes such as 8, 10A, 17F, 22F, 24ABF, 34, and 39.Conclusion. Pneumococcal vaccination decreased prevalence of pneumococcal carriage, yet causing a serotype replacement effect requiring improved microbiological monitoring in children of all age groups.