Presentation (CTI)

OBJECTIVES: Unlike single-dose vaccines, multi-dose vaccines, such as the recently rolled-out malaria vaccines, require sustained interactions with immunization systems to achieve optimal public health impact. However, while malaria vaccine effectiveness is highly dependent on progression through successive doses, most evaluations rely on assumed coverage trajectories that may differ from real-world, society-specific implementation patterns. This study uses recent multi-dose vaccine progression data from Nigeria to develop empirically informed malaria vaccine implementation scenarios and to explore their implications for future malaria vaccine evaluation in Nigeria and other societies.
METHODS: Based on the available data, annual data for the first-dose Pentavalent (Penta1), second-dose Pentavalent (Penta2), and third-dose Pentavalent (Penta3) from the last 3 years (2023 -2025) were extracted and used to calculate dose progression ratios. These ratios were used to inform plausible malaria vaccine implementation scenarios, including high-completion, moderate-attrition, and catch-up scenarios. The analysis focused on vaccine initiation, continuation, and completion rather than timeliness, as individual vaccination dates were unavailable.
RESULTS: While Penta3/Penta1 completion ratios were high across all years: 92.0% in 2023, 94.4% in 2024, and 94.0% in 2025, Penta2/Penta1 ratios were lower, ranging from 84.1% to 86.9%, with Penta3/Penta2 ratios exceeding 100% across all years. These patterns informed three malaria vaccine implementation scenarios: high-completion (~94%), moderate-attrition (~86%), and catch-up (>100% Penta3/Penta2).
CONCLUSIONS: This study revealed that simple monotonic dropout assumptions may not adequately capture Nigeria’s routine immunization dynamics, contrary to what is usually expected. Therefore, as malaria vaccine rollout scales up across Nigeria and similar high-burden societies, such local implementation evidence is explicitly needed to inform health economic models for these interventions and avoid misestimating their true public health value.