Pneumococcal Carriage in Infants Post-PCV10 Introduction in Pakistan: Results from Serial Cross-Sectional Surveys

The 10-valent pneumococcal vaccine was introduced in Pakistan’s Expanded Program on Immunization (EPI) in 2013 as a 3+0 schedule without catchup. We conducted three annual cross-sectional surveys from 2014-2016 to measure vaccine-type (VT) carriage in infants from a rural part of Pakistan. Nasopharyngeal specimens were collected by random sampling of infants from 2 union councils of Matiari. Samples were then transported to Infectious Disease Research Laboratory (IDRL) at the Aga Khan University within 6-8 hours of collection. Serotypes were established using sequential multiplex PCR. Of the 665 children enrolled across three surveys, 547 were culture positive for pneumococcus. VT carriage decreased from 21·8% in 2014 to 12·7% in 2016 (p-value for trend <0·001). Those who were not vaccinated or partially vaccinated were found to be at higher risk of carrying a VT serotype (aOR 2·53, 95% CI 1·39, 4·63 for non-vaccinated) and (aOR 3·35, 95% CI 1·82, 6·16 for partially vaccinated). On the other hand, being enrolled in the most recent survey was negatively associated with VT-carriage (aOR 0·51, 95% CI 0·28, 0·93). We found that PCV10 was effective in decreasing the carriage of vaccine-type serotypes in Pakistani infants.