Emergence of non-vaccine Streptococcus pneumoniae serotypes colonizing the nasopharynx of children under five years of age in the 13-valent pneumococcal conjugate vaccine era in Tanzania. A short communication.

To determine the impact of pneumococcal vaccination on nasopharyngeal carriage in Tanzania, we assessed the serotype distribution of S. pneumoniae isolated from nasopharyngeal swab samples. These samples were collected in 539 children below the age of 5 years in two cross-sectional studies, one before and one after PCV13 rollout. In the second study, post-PCV13 rollout, only children who completed the PCV13 vaccination schedule, were included. From the study conducted before the introduction of PCV13, 61 (55 %) of S. pneumoniae serotypes were vaccine types, compared to 89 (23.3 %) post-PCV13. The most common serotypes in the pre-PCV13 period were 19F (n = 23, 20.7 %) and 6B (n = 11, 9.9 %). In the post-PCV13 era, serotypes 15B/C (n = 40, 10.5 %), and 3 (n = 29, 7.6 %) were most prevalent. We observed the emergence of 14 non-vaccine serotypes not detected in the pre-vaccine era. Further surveillance is needed to assess shifts in carriage and their implications for the protection against invasive pneumococcal disease.