Long-Term Safety and Efficacy of the RTS,S/AS02A Malaria Vaccine in Mozambican Children

Background. We previously reported that the RTS,S/AS02A vaccine had an acceptable safety profile, was immunogenic, and demonstrated efficacy against Plasmodium falciparum malaria disease for 21 months. Methods. We conducted a randomized, controlled, phase 2b trial of RTS,S/AS02A in 2022 Mozambican children aged 1-4 years. We now report safety results for all randomized subjects and vaccine efficacy (VE) findings for children in the Manhica area over the 45-month surveillance period. Results. During the surveillance period, the VE (2 . 5-45) (VE over months 2.5-45 of surveillance) against a first or only episode of clinical malaria disease was 30.5% (95% confidence interval [CI], 18.9%-40.4%; P<.001), and the VE (2.5-45) against all episodes was 25.6% (95% CI, 11.9%-37.1%;P<.001). When the same period was considered, the VE( 2.5-45) for subjects protected against severe malaria was 38.3% (95% CI, 3.4%-61.3%; P = .045). At study month 45, the prevalence of P. falciparum was 34% lower in the RTS,S/AS02A group than in the control group (66 [12.2%] of 541 patients vs 101 [18.5%] of 547 patients) (P = .004). Conclusion. These results show evidence that RTS,S/AS02A maintained protection during the 45-month surveillance period, and they highlight the feasibility of developing an effective vaccine against malaria. In combination with other malaria-control measures, such a vaccine could greatly contribute to reducing the intolerable global burden of this disease.