A new article in Lancet Infectious Diseases reports on the results of a study that aimed to improve understanding of the longer-term impact of the RTS,S/AS01 (RTS,S) malaria vaccine, with a focus on severe malaria. The study, an extended follow-up of the Phase 3 efficacy and safety trial of RTS,S, followed children who previously participated in the Phase 3 trial (from Nanoro, Burkina Faso; Kombewa, Kenya; and Korogwe, Tanzania) for an additional three years (for a total of seven).
Results show that the incidence of severe malaria decreased with increasing age of the children, regardless of whether or not the children received the vaccine, and that there was no evidence of a rebound of severe malaria following the four-dose schedule of the vaccine. Over the entire seven-year post-vaccination period, vaccine efficacy against severe malaria was 36.7 percent [95 percent CI 14.6, 53.1] in children who started their four-dose vaccination schedule at the age of 5 to 17 months. Clinical malaria was reduced by 23.7 percent [95 percent CI 15.9, 30.7] in this age group over the same period. In addition, the study did not raise new safety concerns, and the benefit/risk balance, as previously established during clinical trials, remains unchanged.
In 2015, the efficacy of RTS,S over four years of follow-up was reported. Among children aged 5 to 17 months who received four doses of RTS,S, the vaccine prevented approximately 40 percent of cases of any clinical malaria and about 30 percent of cases of severe malaria. The study reported in the newly published article provides strong evidence that RTS,S can provide sustained protection against severe malaria through seven years of follow-up. The impact and safety of the vaccine in the context of routine use will continue to be evaluated through a World Health Organization-coordinated pilot introduction being implemented by health ministries in areas of Ghana, Kenya, and Malawi.