A booster dose of malaria vaccine candidate R21/Matrix-M shows high efficacy in children, a phase 2b clinical trial reveals.
The phase 2b clinical trial, whose findings were published in The Lancet in 2021, enrolled 450 children aged 5–17 months in Nanoro, Burkina Faso. Of them, 409 received the booster dose.
The participants were given the low dose of circumsporozoite protein-based vaccine R21, with two different doses of adjuvant Matrix-M (MM). Three vaccines were administered at 4-week intervals before the malaria season and a booster dose a year later.
At the 6-month primary efficacy analysis, vaccine efficacy in group 1, which received a lower dose of adjuvant, was 74%, while in group 1, which received a two-times higher dose of adjuvant, efficacy was 77%. The side effects were mild, with the most common being fever.
At one year, vaccine efficacy remained high, at 77% in group 1.
Restored antibody levels
In September 2022, researchers reported the new findings of a phase 2b clinical trial following the administration of a booster dose of R21/Matrix-M 12 months after three-dose primary series.
The new research, published in The Lancet Infectious Diseases, demonstrates vaccine efficacy of 80% in the higher-dose adjuvant group, and 70% in the lower-dose adjuvant group, over 12 months of follow-up.
Researchers say that 28 days after the booster doses were administered, antibody levels were restored to similar levels as those after the primary series. No serious side effects were reported in the trial.
The authors, however, point out that the small sample size of the study restricts the identification of less common adverse events and reduces the power to identify a potential correlate of protection.
Halidou Tinto, Professor in Parasitology, Regional Director of IRSS in Nanoro, and the trial Principal Investigator, said in a press release: “It is fantastic to see such high efficacy again after a single booster dose of vaccine. We are currently part of a very large phase 3 trial aimed at licensing this vaccine for widespread use next year.”
The phase 3 clinical trial assesses large-scale safety and efficacy in 4,800 children aged five to 36 months across four African countries. The results of the trial are expected later in 2022.
Malaria’s burden on Africa
Malaria is a life-threatening disease caused by Plasmodium parasites, which are spread to people through the bites of infected female Anopheles mosquitoes.
In 2020, there were 241 million cases of malaria and 627 000 deaths worldwide, according to the latest World malaria report by the World Health Organization (WHO),
African countries account for more than 90% of malaria cases and deaths. The disease is especially dangerous for infants, children under five years old, pregnant women, patients with HIV/AIDS, and people with low immunity.
To prevent the disease, the WHO recommends a broad use of the RTS,S/AS01 vaccine among children living in regions with moderate to high Plasmodium falciparum – the deadliest parasite species causing the disease – malaria transmission.
In phase 3 clinical trial, the RTS,S/AS01 vaccine, also known as Mosquirix, showed an efficacy of 31.3% in infants aged 6–12 weeks and 55.8% in children aged 5–17 months.
The Lancet Infectious Diseases. 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.
The WHO. Malaria.
The WHO. World malaria report 2021.
MDPI. Mosquirix™ RTS, S/AS01 Vaccine Development, Immunogenicity, and Efficacy.