Strategies for pneumococcal conjugate vaccine use in humanitarian crises

Humanitarian crises substantially increase the health burden in affected populations. Streptococcus pneumoniae is a major cause of morbidity and mortality globally, and likely causes a considerable proportion of the burden in crisis-affected populations. Pneumococcal conjugate vaccines (PCVs) effectively prevent against pneumococcal disease but there is little guidance on their effective and feasible use during humanitarian crises, and they are rarely part of the humanitarian response. I combined primary data collection with mathematical modelling to assess the effect of PCV mass-vaccination campaigns in crisis-affected populations. I first conducted a cross-sectional survey collecting data on social mixing, demography, pneumococcal carriage and related risk factors in a camp for internally displaced people in Somaliland. Social contact patterns were assortative by age with high rates of physical contacts. Most contacts were made at home and by school-aged children. Pneumococcal carriage prevalence was high, especially in children, and was similar to that in other high-transmission settings. Transmission was driven by children aged 2-5 and 6-14 years. I then constructed a pneumococcal transmission model parameterized with the collected data, and assessed the effect of a PCV mass-vaccination campaign in different crisis typologies. Single-dose PCV campaigns vaccinating children aged six weeks to one year only have a limited impact. However, extending vaccination to children aged four years or older can partially disrupt the transmission of serotypes targeted by PCV and prevent a substantial proportion of invasive pneumococcal disease over two to three years. Expanded age eligibility may be needed to control transmission in settings with high migration or interaction with unvaccinated populations. Overall, my research shows that single-dose PCV mass-vaccination campaigns could offer feasible and pragmatic protection against pneumococcal disease to crisis-affected populations where routine immunization may not be possible.