Abstract We examined the validity of the indirect cohort method as a rapid assessment tool to estimate pneumococcal polysaccharide vaccine effectiveness (VE). Using evidence from published clinical trials, we reviewed the primary assumption about the appropriateness of the control group underpinning the indirect cohort method, which is that the risk of non-vaccine type invasive pneumococcal disease is equal for vaccinated and unvaccinated participants. We found an absence of evidence to support the non-differential risk assumption for non-vaccine type invasive pneumococcal disease occurring among clinical trial participants. In those instances where the design has been utilised, we also note that these typically rely on very small numbers of non-vaccine type invasive pneumococcal disease adding to the concerns as an unreliable comparator. We do not consider the indirect cohort method to be a valid tool for rapid assessment of pneumococcal polysaccharide VE.
Keywords: indirect cohort method; pneumococcal polysaccharide vaccine; vaccine effectiveness; pneumococcal disease

Abstract As national immunization programmes, particularly those in low- and middle-income countries where administrative recording of services received is often absent or sub-optimal, enter a period of rapidly paced change with new vaccine introductions, it seems important to identify ways to avoid unnecessary re-vaccination of children and the associated costs. Some re-vaccination may be unavoidable, while other re-vaccination is almost certainly avoidable but nevertheless occurs. Unfortunately, the prevalence and epidemiology of re-vaccination of children are ill-described, and potential risks due to re-vaccination are either nil or also unknown. Nonetheless, it is seemingly important to better understand avoidable re-vaccinations that occur as a result of a breakdown along the service delivery continuum.
Keywords: Home-based vaccination; hypothetical cost-savings; avoidance of re-vaccinating children