Research in context
19F colonisation
DISEASE

Pneumococcal conjugate vaccines (PCVs) remain the most expensive vaccine in routine childhood immunisation programmes. To circumvent costs, considerations are underway to reduce the dosing schedule from a 2 + 1 to a 1 + 1 schedule. The UK became the first country to do so. Careful considerations are needed before transitioning to a reduced dose of PCV in low-income and middle-income countries (LMICs), where residual transmission of vaccine serotypes and the burden of pneumococcal disease remains higher than in high-income countries, such as the UK. To investigate the direct effect of the alternative ten-valent PCV (PCV10) or 13-valent PCV (PCV13) schedules on the serotype-specific pneumococcal carriage, we did a systematic literature review using PubMed to identify clinical studies published in English up to Oct 17, 2022, using the search terms “pneumococcal conjugate vaccines” or “PCV10” or “PCV13”, and “dosing schedule” or “alternate dosing schedule” or “reduced dosing schedule”, and “carriage” or colonization”, and “pneumococcus” or “
To our knowledge, our study is the first to analyse new acquisition and carriage of vaccine serotypes and non-vaccine serotypes following the booster dose of PCV in children receiving a single priming dose compared with those who received two priming doses of PCV10 or PCV13. The study shows no difference in the acquisition of new vaccine or non-vaccine serotypes between the study groups for both vaccine formulations. We also report lower prevalence of vaccine serotype colonisation post booster in the PCV13 group that received a priming dose at 14 weeks of age and booster at 9 months of age compared with the 2 + 1 group, which received priming doses at 6 weeks and 14 weeks of age and a booster at 9 months of age, particularly for serotype 19F (2·9-fold lower). These results mitigate concerns of a delayed primary series (at 14 weeks only) increasing the incidence of vaccine serotype carriage acquisition and risk of invasive pneumococcal disease in young infants, in whom the first carriage episode can occur within the first few weeks of life in LMICs. Transitioning to a PCV13 1 + 1 dosing schedule, with the priming dose at 14 weeks, in South Africa could translate to better protection against 19F colonisation and the risk of 19F invasive pneumococcal disease in settings such as ours.
PCV immunisation must remain cost-effective in a mature immunisation programme in places where the risk of pneumococcal disease is already reduced at a population level. The serotype-specific colonisation data reported in this study, together with the primary immunogenicity endpoints of the control trial, support transitioning to a reduced 1 + 1 schedule in South Africa. This will make PCV procurement more affordable, with little risk of increased acquisition of vaccine serotypes, which are usually the most prevalent, invasive, and antibiotic-resistant types in children. Ongoing surveillance of colonisation trends will be necessary as an early indicator of whether transitioning to a 1 + 1 schedule might lead to an increase in the risk of vaccine-serotype disease.