Pneumonia remains a leading killer of children under the age of five globally, with the heaviest burden in developing countries. Vaccines are available for the most common cause of pneumonia, Streptococcus pneumoniae (the pneumococcus). However, resource-poor countries face challenges in implementing a full vaccination program due to their considerable cost and the lack of coverage provided by current vaccines against serotypes that cause significant proportions of disease in these settings.
The Fiji Pneumococcal Project (FiPP) examined the effects of different immunisation schedules, in particular whether fewer doses of the pneumococcal protein conjugate (PCV7) vaccine combined with the polysaccharide (23vPPS) vaccine could provide adequate protection in children. A key finding from the study was the induction of immune hyporesponsiveness in children who received a 12 month 23-valent polysaccharide dose. Children from the FiPP trial are now being followed-up to assess the long term impact of the polysaccharide vaccine.
The focus of this project is to assess pneumococcal carriage and how this relates to host immunity. To determine the long-term effect of the polysaccharide vaccination, nasopharyngeal swabs (n=215) were obtained from children now aged 4-6 years. Using traditional culture and serotyping methods, the pneumococcal carriage rate was found to be 48%. This is similar to that found in the original study, which was unexpected as pneumococcal carriage declines with age. Of 123 pneumococcal isolates identified, 36 different serotypes were present. Of these, 11A (8%), 16F (7%), 6A (7%) and non-typeable (17%) were the most common. The carriage densities of pneumococci and other bacterial species will be determined by qPCR.
Further investigation and analysis will be required to understand the long term impact of vaccination with 23-valent polysaccharide vaccine including completing a comparative analysis with immunology data and relationship to vaccination status.