The ten-valent pneumococcal conjugate vaccine (PCV10) was introduced in Nepal in 2015. We compared the nasopharyngeal carriage of PCV10 and non-PCV10 serotypes of pneumococcus between pre-vaccine (2015) and post-vaccine (2017-2018) years in two different regions of Nepal.
Nasopharyngeal samples obtained in healthy Nepalese children aged 6-59 months in urban (Patan, Kathmandu) and 6-23 months in rural (Okhaldhunga) settings were transported in STGG (Skim Milk-Tryptone-Glucose-Glycerol) media, cultured for pneumococcus and serotyped by the Quellung method.
The carriage prevalence decreased for all PCV10-type serotypes except 7F in both the settings. PCV10-type prevalence decreased from 29.7% in rural and 17.2% in urban children pre-vaccine to 9.0% and 8.6% post-vaccine, respectively. Pre-vaccine, the most frequently found serotypes in both settings were 19F, 6B, 14. Post-vaccine, the non-PCV10 serotypes were more common; serotypes 34, 6C, 19A and 15B were most common in rural and 6A, 34, 11A, 6C and 15B in urban settings.
Since the introduction of PCV10, carriage prevalence of PCV10 serotypes have reduced and non-PCV10 serotypes have increased in both settings raising the possibility of replacement disease. Continued monitoring of changes in PCV10-serotypes and non-PCV10 serotypes, especially those covered by PCV13, is important to assess vaccine impact.