The impact of the RTS,S malaria vaccine on uncomplicated malaria: evidence from the phase IV study districts, Upper East Region, Ghana, 2020-2022

Background The RTS,S malaria vaccine has been prequalified for use in endemic settings prioritizing areas with moderate to high disease transmission. The impact of a vaccine at the population level may differ from observations during clinical trial due to programmatic, and individual-related factors, among others. The objective of this study was to assess the impact of the RTS,S malaria vaccine on uncomplicated malaria among children aged 12-59 months in the Phase IV study districts, Upper East Region, Ghana. Methods A retrospective study was conducted using routine malaria surveillance data for the period 2020-2022. The burden of uncomplicated malaria was compared between the implementing (Kasena Nankana East and West districts) and comparator areas (Builsa North and South districts). The impact of RTS,S malaria vaccine was assessed by estimating the percentage reduction in uncomplicated malaria and incidence averted in the implementing area, accounting for the effect of confounders. Results Over 50,000 episodes of uncomplicated malaria among children aged 12-59 months were included in the study. Uncomplicated malaria was reduced by 33% (95%CI 29-36) over the entire study period, but the malaria incidence averted declined from 324/1,000 (95% CI 298-339; p < 0.0001) in 2020 to 287/1000 (95% CI 274-299; p < 0.0001) in 2022. Conclusion The RTS,S malaria vaccine significantly reduced the burden of uncomplicated malaria among children aged 12-59 months in the implementing area. The sequential marginal declines in malaria incidence averted over the study period might be due to waning of protective immunity and acquisition of natural immunity as children age. Strengthening uptake of the currently recommended vaccines and other malaria control interventions is required to improve public health impact.