Project Details

RTS,S/AS01 Malaria vaccine performance across ecological zones of Cameroon: Differential Effectiveness, Halo Effects, and Risk Compensation

Cavin Epie Bekolo, MD, MSc, PhD

Summary

BACKGROUND: Malaria is a major cause of morbidity among children under five in Cameroon, responsible for a substantial proportion of hospitalisations and outpatient consultations. In 2024, children under five accounted for 40.6% of all malaria-related consultations in health facilities. Transmission varies across three ecological zones: equatorial forest (perennial high), western highlands (moderate seasonal), and Sahelian (intense seasonal, where Seasonal Malaria Chemoprevention – SMC – is implemented). GAP: No study has evaluated the effectiveness of RTS,S/AS01 across Cameroon's ecological zones, its incremental benefit in SMC areas, or its systemic effects on other vaccines and caregiver behaviour. HYPOTHESIS: RTS,S/AS01 reduces paediatric hospitalisations, malaria, and severe anaemia, with larger effects in forest zones and measurable added benefit beyond SMC in Sahelian zones. Vaccine introduction improves completion of other vaccines and reduces non-malaria morbidity (halo effects), while some caregivers reduce net use (risk compensation). METHODS: Quasi-experimental, controlled before-after study with Difference-in-Differences analysis across Mfou (forest), Foumbot (highlands), and Mokolo (Sahelian) districts. Monthly hospitalisation data will be extracted (12 months pre-vaccine, 24 months post-vaccine). A survey of 1,200 caregivers (400 per zone) with point-of-care haemoglobin testing will be conducted. RESULTS: Pending. IMPACT: This study will provide the first zone-specific evidence of the real-world effectiveness of RTS,S/AS01 in Cameroon, including its added value in SMC areas. Findings on halo effects and risk compensation will inform integrated child health strategies across sub-Saharan Africa.