Long-term impact of 10-valent pneumococcal conjugate vaccine in Kenya: Nasopharyngeal carriage among children in a rural and an urban site six years after introduction

Abstract

Background: Kenya introduced Synflorix™ (GlaxoSmithKline, PCV10-GSK), a 10-valent pneumococcal conjugate vaccine, in 2011, using three primary doses and, in select areas, catch-up campaigns. Surveys conducted 1-2 years post-introduction showed a stable prevalence of pneumococcal colonization, with declines in vaccine-type carriage. However, little is known about the long-term impact of PCV10-GSK in Kenya.

Methods: We conducted a cross-sectional survey of pneumococcal carriage among children aged <5 years in November-December 2017 in Kibera (Nairobi informal settlement, no catch-up) and Asembo (rural western Kenya, 2-dose catch-up for children 1-4 years), using the same methods and settings as prior annual surveys from 2009 to 2013. Participants were randomly selected from an ongoing population-based surveillance platform. Nasopharyngeal swabs were frozen in skim milk-tryptone-glucose-glycerin media within 4 h and underwent culture with broth enrichment for pneumococcus. Isolates were serotyped by polymerase chain reaction and Quellung.

Results: We enrolled 504 children, including 252 from each site; >90 % of participants had received 3 doses of PCV10-GSK. Pneumococcal colonization was detected in 210 (83.3 %) participants in Kibera and 149 (59.1 %) in Asembo, which was significantly lower than the prevalence observed in 2013 (92.9 % and 85.7 %, respectively). PCV10-GSK serotypes were detected in 35/252 (13.9 %) participants in Kibera and 23/252 (9.1 %) in Asembo, respectively; these prevalences were lower, but not statistically different, from vaccine-type carriage prevalences in 2013 (17.3 % and 13.3 %, respectively). In 2017 in both sites, serotypes 3, 6A, 19A, 19F, and 35B were among the most common serotypes.

Conclusion: Six years post-PCV10-GSK introduction, the prevalence of pneumococcal carriage among children has decreased, and the impact of PCV10-GSK on vaccine-type carriage has plateaued. Kenya recently changed from PCV10-GSK to Pneumosil™ (Serum Institute of India), a 10-valent PCV that includes serotypes 6A and 19A; these data provide historical context for interpreting changes in vaccine-type carriage following the PCV formulation switch.

Keywords: Child; Kenya; Pneumococcal carriage; Pneumococcal vaccines; Streptococcus pneumoniae.

Fig. 1

Pneumococcal carriage among children aged < 12 months (A) and 12–59 months (B), Asembo and Kibera, Kenya, 2009–2013 and 2017. Numbers at the base of each bar reflect number of participants. *p value < 0.05 comparing 2017 to 2013.

Fig. 2

Vaccine-type pneumococcal carriage among children < 12 months (A) and 12–59 months (B), Asembo and Kibera, Kenya, 2009–2013 and 2017. Numbers at the base of each bar reflect number of participants.

Fig. 3

Serotype frequency among carriage isolates from children aged < 5 years in Kibera (A, n = 223 isolates) and Asembo (B, n = 153 isolates), 2017 *Included in PCV10-SII. ^†Not included in PCV10-SII.

Fig. 4

Relative frequency of vaccine serotypes among carriage isolates from children aged < 5 years in Kibera in Kibera (A) and Asembo (B), in 2013 and 2017. Kibera isolates were n = 450 in 2013 and n = 223 in 2017; Asembo isolates were n = 183 in 2013 and n = 153 in 2017. *Included in PCV10-SII. ^†Not included in PCV10-SII.