Effect of the 13-valent pneumococcal conjugate vaccine on nasopharyngeal carriage by respiratory pathogens among Greenlandic children

Background: In 2010, Greenland introduced the 13-valent pneumococcal conjugate vaccine (Prevnar 13 (R) - PCV-13) in the childhood immunisation program. The authors aimed to evaluate the impact of PCV-13 on nasopharyngeal carriage of bacteria frequently associated with respiratory infections in children. Method: In 2013 a cross-sectional population-based study of nasopharyngeal carriage was conducted among Greenlandic children aged 0-6 years and results were compared with an equivalent study from 2011. Nasopharyngeal swab samples were tested for Streptococcus pneumoniae, non-typeable Haemophilus influenzae, Moraxella catarrhalis and Staphylococcus aureus. Pneumococcal serotyping was performed by Quellung reaction and serotype-specific antisera. Statistical analysis included logistic regression models, adjusting for known risk factors. Result: A total of 377 nasopharyngeal samples were collected. Overall carriage rate of S. pneumoniae remained unchanged from 2011 to 2013 (51% and 56%, p=0.13), but significant serotype shifts were observed among both vaccinated and unvaccinated children with marked reductions in carriage of vaccine-type pneumococci, counterbalanced by increasing carriage of non-vaccine types. Carriage rate of S. aureus decreased significantly among vaccinated children whereas that of M. catarrhalis increased. Conclusion: PCV-13 introduction in Greenland is associated with significant changes in nasopharyngeal bacterial carriage. Continued surveillance is warranted to clarify whether these changes are persistent, and affect the pattern of respiratory and invasive diseases in Greenland.