Malaria forms a major cause of hospital admissions and death among young children in many African countries.Recently, two malaria vaccines were approved by the World Health Organization (WHO) to help reduce the burden of disease in children in malaria-endemic counties. These vaccines are called RTS,S/AS01E and R21/Matrix-M. While these vaccines provide a high level of protection during the first months after vaccination, their effectiveness decreases over time. The WHO therefore recommends that at least one booster dose of the respective vaccine is given to children ~1 year after their initial vaccination series (priming doses), in order to maintain protective immunity.
In some areas of Africa, such as the Sahel, malaria transmission is highly seasonal, occurring only during the rainy season. In such settings, it has been shown that malaria vaccine booster doses have an additive protective effect against malaria episodes in children, on top of established control measures such as seasonal malaria chemoprevention (SMC). However, some debate remains about the best way to implement malaria vaccine booster doses to achieve the highest efficacy. Specifically, it is unclear whether it makes most sense to implement an age-based or seasonal boosting strategy. Age-based boosting is a strategy in which booster doses are administered at a fixed age, and thus at a fixed time since the child's initial malaria vaccinations, similar to schedules for other childhood vaccines. Seasonal boosting means to provide booster doses to all children at the same time of year, immediately prior to the malaria transmission season, regardless of the child's age and thus of the time since its initial malaria vaccinations. Another potential concern is that the uptake of vaccine booster doses in children over 1 year of age may be lower than desired. It is therefore unclear whether seasonal booster doses should simply be made available at routine childhood vaccination clinics, or if higher coverage can be achieved through community mass vaccination campaigns.
In this Seasonal Malaria Vaccination (SMV) Delivery project we will address these two questions: (1) In Guinea, we will compare the coverage achieved with seasonal boosters (administered in June, prior to transmission season) with that of age-based boosters (administered 1 year after the third priming dose vaccine, regardless of the calendar month) and their respective effect on malaria incidence in young children; (2) In Mali, we will determine whether annual pre-transmission season boosters given through a door-to-door mass community campaign achieves better vaccination coverage and impact on malaria incidence in young children compared to provision of these booster doses at routine childhood vaccination centers. These questions will be investigated through implementation studies in selected districts in Mali and Guinea. This project will thereby provide important information on the optimum delivery of malaria vaccination booster doses in settings of seasonal malaria transmission, which could save many lives.
