Effectiveness of pneumococcal vaccination campaigns in humanitarian settings: A modelling study

Background A large and increasing number of people are forcibly displaced worldwide because of war, food insecurity, and other crises. Streptococcus pneumoniae likely causes a substantial health burden in crisis-affected populations. Pneumococcal conjugate vaccines (PCVs) are widely used in routine immunisation programmes, including through the Essential Programme on Immunization (EPI) to protect against pneumococcal disease. They are typically administered as a three-dose schedule, either as three doses in early infancy or two doses in infancy followed by a booster at 9–18 months of age. However, PCVs are rarely used in humanitarian responses. We evaluated the potential impact of logistically feasible PCV campaigns in such settings. Methods and findings We conducted a pneumococcal carriage, malnutrition, and social contact survey in a camp for displaced people near Hargeisa, Somaliland, to parameterise a transmission model accounting for migration. We projected the effect of PCV mass-vaccination campaigns using one or two doses and vaccinating children <1, 2, 5, 10, or 15 years (y) of age in the Somaliland camp and three different crisis settings. We found that a single-dose PCV campaign with high vaccine coverage in children <5 y or older can partially control vaccine-serotypes for up to 3 y, preventing 27% (95% CrI: 20, 34) of severe pneumococcal disease, defined as a composite of invasive pneumococcal disease and nonbacteraemic pneumonia, when vaccinating <5 y olds and 38% (95% CrI: 29, 46) when vaccinating <15 y olds. Expanded age eligibility is needed for comparable protection in settings with increased migration or more interaction with unvaccinated host populations. A campaign vaccinating <5 y olds is the most efficient use of PCV with 108 (95% CrI 77–162) vaccines needed to prevent one case of severe pneumococcal disease. Implementing such campaigns in displaced populations worldwide would require about 30 million doses in the next 5 y. Key limitations included sparse empirical data on PCV effectiveness and pneumococcal disease in humanitarian settings, and extrapolation of Somaliland carriage and contact patterns to other crisis settings. Conclusions Single-dose mass-vaccination campaigns offer crisis-affected populations an effective, pragmatic immunisation strategy to deliver PCVs if routine EPI services have been disrupted.