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R21/Matrix-M vaccine protective against malaria in children over 2 year period

13th September 2022

The R21/Matrix-M vaccine provides acceptable efficacy against malaria in children two years after the primary vaccination regime

The malaria vaccine, R21/Matrix-M has been shown to provide a high degree of efficacy against the disease in children, two years after the initial primary vaccination regime and a 12 month booster according to the findings of a study by a research team based at the Jenner Institute, University of Oxford and in collaboration with researchers from Burkina Faso.

Malaria is a life-threatening disease caused by Plasmodium falciparum (P falciparum), a parasite that is transmitted via the bite of infected female Anopheles mosquitoes that is both preventable and curable. According to the World Health Organisation (WHO), in 2020, there were an estimated 241 million global cases of malaria and 627 000 deaths. Moreover, in a 2021 report WHO noted how Sub-Saharan Africa continues to carry the heaviest malaria burden, accounting for about 95% of all malaria cases and 96% of all deaths in 2020. Additionally, about 80% of deaths in the region are among children under 5 years of age. WHO set a target in 2013 that a vaccine for malaria should show greater than or equal to 75 percent efficacy. Previous work demonstrated that three vaccination of low-dose R21/Matrix-M, administered at 4-week intervals before the malaria season, with a fourth dose 1 year later, provided an efficacy of 77%.

In the current study, the same research group who undertook the original, randomised, placebo-controlled trial with the R21/Matrix-M vaccine, have provided an update, reporting on the vaccine efficacy over the 12 months following the first booster, i.e., a 24 month period after the primary vaccination regime. The researchers used a primary case definition of clinical malaria as an axillary temperature of 37·5°C or greater.

R21/Matrix-M efficacy against malaria in children

The researchers included 409 children with a mean age of 11.6 years (49% male) at their first vaccine dose and who were followed after their 12 month booster dose, administered before the second malaria season. The data set included 132 given the low dose, group 1 (5 μg R21 adjuvanted with 25 μg Matrix-M), 137 the higher dose, group 2 (5 μg R21 adjuvanted with 50 μg Matrix-M) and 140 who received a control vaccine. Adequate use of insecticide-treated nets before the second malaria season was 89% overall and indoor residual spraying was done in 43% of households.

Based on the primary case definition, there were 242 cases with at least one episode of malaria from 14 days to 12 months after the booster vaccination. Among those in group 1, this represented a vaccine efficacy of 70% (95% CI 59 – 78) and 80% (95% CI 72 – 85) in group 2 compared the control group, after adjustment for sex, age and adequate bednet use.

When researchers re-assessed R21/Matrix-M at 24 months after the primary vaccination regime, the vaccine efficacy was 66% (95% CI 55 – 74) for group 1 and 75% (95% CI 66 – 81) for group 2.

The authors concluded that when delivered seasonally, the R21/Matrix-M malaria vaccine maintained high efficacy and that these findings suggest the vaccine strategy could have a substantial impact in areas of highly seasonal malaria transmission in Africa.

Citation
Datoo MS et al. Efficacy and immunogenicity of R21/Matrix-M vaccine against clinical malaria after 2 years’ follow-up in children in Burkina Faso: a phase 1/2b randomised controlled trial Lancet Infect Dis 2022

Malaria vaccine candidate achieves 77% efficacy in children

27th April 2021

With only a single malaria vaccine with limited efficacy, the search continues for more effective agents.

The parasite Plasmodium falciparum (P. falciparum) is responsible for malaria and which is a leading cause of both morbidity and mortality across the globe. RTS,S, brand name Mosquirix, is the only vaccine available to treat malaria and was approved by the EMA in 2015. Sporozoites are the form of the parasite that enter the body and Mosquirix contains part of the P. falciparum circumsporozoite protein (CSP) and leads to the generation of anti-circumsporozoite antibodies. However, in children, the vaccine efficacy is only 56% whereas the World Health Organization’s strategic goal is for a malaria vaccine to have an efficacy of 75%. This led researchers from the Jenner Institute, University of Oxford to undertake a double-blind, randomised, controlled trial using a vaccine named R21, which is a novel pre-erythrocytic candidate that also targets part of the CSP. The vaccine combines R21 with Matrix-M (MM), an adjuvant which increases immunogenicity. The team recruited children aged 5–17 months in the catchment area of Nanoro, Burkina Faso (West Africa) and which represents a high area of malaria transmission, especially between June and November. All children were randomised to one of three groups; group 1 received a lower dose of MM (i.e., 5 mcg R21/25mcg MM); group 2, a higher dose of MM (5 mcg R21/50mcg MM); and a control group (group 3) who received a control vaccine (rabies). Three doses were administered at 4-week intervals prior to the main malaria season (early May to August) and all participants received a fourth booster dose 12 months after their third vaccination. The primary outcome assessed was protective efficacy from 14 days after the third vaccination to 6 months and clinical malaria was defined in terms of an axillary temperature greater than 37.5 degrees centigrade and a P. falciparum density of greater than 5000 parasites/micro-litre.

Findings
A total of 450 children were included in the trial with a mean age of 11.6 months and 222 female participants. Moreover, there were 186 cases of clinical malaria, 43 in group 1, 38 in group 2 and 105 in group 3 (control). Using a Cox regression model which compared group 1 to 3, vaccine efficacy was 74% (95% CI 63 – 82, p < 0.001) and between group 2 and 3, the efficacy was 77% (95% CI 67 – 84, p < 0.0001). Efficacy was also assessed after 12 months at which point, the efficacy was 71% (group 1 vs group 3) and 77% (group 2 vs group 3). The authors calculated that the number of cases averted by the group 1 regime over 12 months would be a rate reduction of 1393 cases per 1000 children years.

The authors observed, however, that antibody levels in groups 1 and 2 decreased over the 12-month period but were boosted back to the levels achieved after the third dose, 28 days after the 4th dose.

Although this is the first study to report on the vaccine, the trial is continuing for a second malaria season to determine the durability of this high level of vaccine efficacy.

Citation
Datoo MS et al. High efficacy of a low dose candidate malaria vaccine, R21 in adjuvant Matrix-MTM, with seasonal administration to children in Burkina Faso. Lancet 2021