In a significant step forward in the fight against malaria, the RH5.1/Matrix-M vaccine has shown promising results in a phase 2b trial conducted in Burkina Faso. The study, involving 361 children aged 5-17 months, assessed the safety, immunogenicity, and efficacy of the vaccine in a seasonal malaria transmission setting.
Participants were divided into two cohorts, receiving either the RH5.1/Matrix-M vaccine or a rabies control vaccine, Rabivax-S, in different dosing regimens. The first cohort received vaccinations in a delayed third-dose regimen (0, 1, and 5 months), while the second cohort followed a monthly regimen (0, 1, and 2 months). The study was double-blind, randomized, and controlled, with only pharmacists aware of the vaccine allocations.
The findings revealed that the RH5.1/Matrix-M vaccine had a favorable safety profile, with most adverse events being mild, such as local swelling and fever. No serious adverse events were reported. The vaccine demonstrated a 55% efficacy in the delayed third-dose regimen compared to the control groups, with a slightly lower efficacy of 40% in the monthly regimen.
High concentrations of anti-RH5.1 serum IgG antibodies were observed in participants 14 days after the third vaccination, indicating strong immunogenicity. The purified IgG from vaccinated participants showed significant in vitro growth inhibition activity against Plasmodium falciparum, the parasite responsible for malaria. This activity was notably higher in the delayed third-dose regimen group.
The ongoing trial, registered with ClinicalTrials.gov (NCT05790889), continues to monitor the vaccine's efficacy over time. These results suggest that the RH5.1/Matrix-M vaccine could be a valuable tool in combating malaria, especially in regions with seasonal transmission patterns.
