Malaria vaccine continues to show promise
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Researchers reported more promising data on a malaria vaccine that previously demonstrated high efficacy among children aged 5 to 17 months in a study published last year.
The vaccine remained highly efficacious 1 year after the children received a booster dose of the vaccine, according to new data published this week in The Lancet Infectious Diseases. The booster shot was given 1 year after the children received an initial three-dose primary series of the vaccine, R21/Matrix-M.
As reported last year, those first three doses demonstrated 77% efficacy among children enrolled in the study, which was conducted in Burkina Faso. After a booster shot, the vaccine continued to meet WHO’s Malaria Vaccine Technology Roadmap goal of a vaccine with at least 75% efficacy.
“It is fantastic so see such high efficacy again after a single booster dose of vaccine,” Halidou Tinto, PhD, a professor of parasitology and regional director of the Health Sciences Research Institute in Nanoro, Burkina Faso, said in a press release.
Between 2019 and 2020, the number of malaria cases worldwide increased by 6% and the number of malaria-related deaths increased by 12% globally, with most of the cases in the African region and 80% of deaths occurring in children aged younger than 5 years, Tinto and colleagues noted in the new study.
WHO recommended a malaria vaccine for the first time last year. The vaccine, RTS,S/AS01, was shown to reduce malaria by 30%.
“There is still a need to identify and develop additional malaria vaccines to allow both increased vaccine supply to ensure maximum coverage of the target population and to enable the WHO goal of a malaria vaccine candidate with 75% or greater efficacy against clinical malaria to be achieved by 2030,” Tinto and colleague wrote.
The initial double-blind phase 1/2b randomized controlled trial enrolled 450 children from the area of Nanoro between May and June 2019. Tinto and colleagues split the participants into three groups — two groups that received the vaccine and either a low- or high-dose adjuvant, and a control group that received a rabies vaccine. They administered three doses 4 months apart from May to early August 2019 — before the peak of malaria season.
Between June 2 and July 2, 2020, 409 children returned to receive a booster dose of the same vaccine they originally received.
Ultimately, the booster’s efficacy was 80% in the high-adjuvant dose group and 71% in the low-adjuvant group. Altogether, 51% of the patients in the low-dose adjuvant group, 39% in the high-dose adjuvant group and 86% in the control group developed clinical malaria by 12 months.
The authors said the findings spurred a phase 3 licensure trial, which has enrolled 4,800 children at five sites across Africa to further test the vaccine’s safety and efficacy. Tinto said the aim is to license the vaccine for widespread use next year.
“Together with maintained high efficacy, these findings suggest that this malaria vaccine and vaccination strategy could have a substantial impact in areas of highly seasonal malaria transmission in Africa [whose] areas account for about half of all childhood deaths from malaria,” the researchers wrote.
References:
Datoo MS, et al. SSRN. 2021;doi:10.2139/ssrn.383068.
Malaria booster vaccine shows durable high efficacy in African children, meeting WHO-specified 75% efficacy goal. https://www.ox.ac.uk/news/2022-09-08-malaria-booster-vaccine-shows-durable-high-efficacy-african-children-meeting-who. Published Sept. 8, 2022. Accessed Sept. 8, 2022.
Perspective
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This is the second major report on the R21 malaria vaccine, which uses the same antigen (portions of the Plasmodium falciparum circumsporozoite protein) as the better-studied RTS,S vaccine but has important differences in composition. RTS,S was developed over the last 2 decades and has demonstrated modest (approximately 30% to 50%) protective efficacy in African children, but availability remains limited, and a more efficacious vaccine would offer a valuable advance.
In a report published last year, administration of the R21 vaccine to children as three monthly doses before the malaria transmission season in Burkina Faso led to an approximately 75% decrease in the incidence of malaria. The new report in The Lancet Infectious Diseases provides extended efficacy results in the same children after a single booster was provided in the year after initial vaccine administration. Results remained very promising, with 71% to 80% decreases in malaria incidence compared with controls, with the higher efficacy in those receiving a higher dose of adjuvant and efficacy correlated with levels of antibodies against the vaccine antigen.
These results suggest that the R21 vaccine may be a valuable new tool against malaria, but available results are most relevant for areas, such as Burkina Faso, with highly seasonal malaria. Larger and longer term studies of vaccine efficacy and safety at sites with varied patterns of malaria transmission, as are now ongoing, are needed to determine the appropriate role for this or other vaccines among the multiple tools now available for malaria control.
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