Residual colonization by vaccine serotypes in rural South Africa four years following initiation of pneumococcal conjugate vaccine immunization

Abstract

ABSTRACT Background We evaluated pneumococcal colonization in children and adults between the time of 7-valent pneumococcal conjugate vaccine (PCV) introduction in the immunization program in 2009 to two years after transitioning to PCV13 in 2011. Methods Community-based carriage surveillance was undertaken between May-November 2013 (Period-3), with similar surveys in 2009 (Period-1) and 2011 (Period-2). Households with children below two years had a similar probability of being sampled in all surveys. Nasopharyngeal swabs were processed using standard methods and serotyped by Quellung. Results In children>9-59 months old, overall pneumococcal colonization prevalence declined from 81.8% in Period-1 to 65.0% in Period-3 (p<0.001). Reductions of 70% (41.2% vs. 13.6%) in PCV7-serotypes colonization and 66% (15.3% vs. 4.4%) for the six additional PCV13-serotypes (PCV13-add6VT) were observed. There was, however, high residual colonization by PCV7-serotypes 19F (14.9% vs. 6.3%) and 23F (8.5% vs. 4.1%), despite reduction of 57% and 52%, respectively. Among individuals>12 years of age, there was 61% reduction in PCV7-serotype colonization (3.1% vs. 1.3%) and 75% decrease for PCV13-add6VT (2.1% vs. 0.6%) between Period-1 and Period-3. Conclusions The residual prevalence of serotypes 19F and 23F, four years after introducing PCV in the South Africa, suggests ongoing community transmission and transient vaccine effects.