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O060 - POPULATION IMMUNITY TO PNEUMOCOCCAL SEROTYPES IN KILIFI, KENYA, BEFORE AND 5 YEARS AFTER THE INTRODUCTION OF PCV10 WITH A CATCH-UP CAMPAIGN (ID 870)
Abstract
Background
In Kilifi, PCV10 was introduced in 2011 with a catch-up campaign in 1-4 year olds. Carriage of vaccine serotypes declined by 64% in children aged <5 years within 6 months of introduction. We aimed to measure the effect of PCV on population immunity.
Methods
Cross-sectional serosurveys were conducted in independent random samples of 500 individuals aged <15 years in 2009, 2011, 2013, 2015 and 2017. Anti-capsular IgG against vaccine serotypes 1, 4, 5, 6B, 7F, 9V, 14, 18C, 19F, 23F and serotypes 6A and 19A, was assayed by ELISA at a WHO reference laboratory. The GMCs and the proportion with an antibody concentration >0.35mcg/ml were examined. Age-specific immunity profiles were constructed by plotting GMCs by birth-year and age.
Results
Vaccine introduction with catch-up increased the proportion of infants and young children with protective levels of IgG. As the vaccination programme matured, GMCs among infants remained high. However, among those vaccinated in infancy, GMCs for 7 of the 10 vaccine serotypes waned rapidly after vaccination, between 1-3 years of age. GMCs rise again later in childhood; there was no change in the GMCs in the oldest age group, 10–14-year-olds, over time.
Conclusions
After PCV10 vaccination in infancy there was relatively rapid waning of IgG for most vaccine serotypes in the first two years of life. However, antibody concentrations remained high in older children throughout the study, despite hypothesised reduced natural boosting in this age group. Continued exposure to vaccine serotypes, e.g., as sub-dominant carriage, or memory responses to cross-reactive antigens could explain this phenomenon.