Impact Of Introducing RTS,S/AS01E Malaria Vaccine On Mortality In Young Children In Ghana, Kenya, And Malawi: An Observational Evaluation Of A Cluster-Randomised Implementation Programme

Abstract

Background: Malaria vaccines have been added to immunisation schedules in 25 sub-Saharan African countries, with the expectation that deaths in young children would be prevented. The introduction of the RTS,S/AS01E malaria vaccine (RTS,S) in Ghana, Kenya, and Malawi in 2019 was evaluated over 4 years to show the impact on mortality in young children and to monitor severe malaria admissions, vaccine uptake, and safety. Favourable evidence on safety and impact on severe malaria admissions during the first 2 years contributed to WHO’s recommendations on malaria vaccines. Here, we report the primary analysis of the impact on mortality at 46 months. Methods: Clusters of administrative units (districts in Ghana, subcounties in Kenya, and groups of immunisation clinics in Malawi), each with an estimated annual birth cohort of about 4000 children, were randomly assigned 1:1 to introduce the RTS,S malaria vaccine in 2019 (implementation areas), or to implement later (comparison areas). RTS,S was delivered in a four-dose schedule, at age 6, 7, 9, and 24 months in Ghana and Kenya, and at age 5, 6, 7, and 22 months in Malawi. Surveillance for post-neonatal mortality in children younger than 5 years was established throughout by a network of 26 000 local reporters who notified deaths in their community. The families were then visited at home by study staff to confirm details and complete a verbal autopsy. Surveillance for severe malaria and other conditions was strengthened in 18 sentinel hospitals serving part of the study area and maintained for 46 months. Uptake of RTS,S and other vaccines was monitored by the Expanded Programme on Immunisation in each country and independently through three household coverage surveys, at baseline, and at about 18 months and 30 months after introduction of RTS,S. The primary outcome of this impact evaluation was mortality due to any cause, except injury, in children eligible to receive three doses of RTS,S. Mortality rate ratios were estimated by comparing the ratio of deaths among vaccine-eligible age groups to deaths in non-eligible age groups between implementation and comparison areas. This evaluation is registered on ClinicalTrials.gov (NCT03806465) and is complete. Findings: 158 clusters (66 in Ghana, 46 in Kenya, and 46 in Malawi) were selected and randomly assigned; 79 areas served as implementation areas and 79 as comparison areas. By the end of the 46-month evaluation period, 1 289 504 children had received the first dose of RTS,S, 1 158 850 had received the second dose, 1 068 039 had received a third dose, and 436 527 had received a fourth dose. Coverage assessed in 2022 was 82·8% (95% CI 80·7–84·9) for the first dose, 71·1% (68·8–73·5) for the third dose, and 39·9% (36·9–42·9) for the fourth dose. Excluding deaths due to injury, there were 5576 deaths in implementation areas versus 6152 in comparison areas in children eligible to have received the third dose of RTS,S, and 7534 versus 7044 deaths among non-eligible children. The mortality rate ratio was 0·87 (95% CI 0·77–0·97; p=0·016). Interpretation: Introduction of the RTS,S malaria vaccine in routine immunisation programmes was associated with a significant reduction in mortality in young children, averting about one in eight deaths, in areas with moderate coverage of three doses of the vaccine and low uptake of the fourth dose. These results highlight the urgency to accelerate the deployment of malaria vaccines in areas of Africa where malaria continues to be a leading cause of child mortality.