This is a clinical trial in which healthy volunteers will be administered one or two experimental malaria vaccines. The vaccine R21 will either be administered alone or in combination with the adjuvant vaccine Matrix-M1.

All vaccinations will be administered intramuscularly. Each volunteer will receive three vaccinations in total.

There are three different vaccine schedules:

Group 1 will receive 10µg of R21 mixed with 50µg of Matrix-M1 on days 0, 28, and 56.

Group 2 will receive 50µg of R21 on days 0, 28, and 56. .

Group 3 will receive 50µg of R21 mixed with 50µg of Matrix-M1 on days 0, 28, and 56.

The study will assess the safety of the vaccines, and the immune responses to the vaccinations. Immune responses are measured by tests on blood samples.

Results

The results of this Phase 1 study showed the vaccinations were well tolerated, and the majority of local and systemic adverse events were mild. Reactogenicity was significantly lower in Burkinabe than UK vaccinees (p<0.0001). Antibody responses increased significantly 28 days after the 2nd vaccination in UK volunteers. Antibody responses to R21 in all dose groups (2μg, 10μg and 50μg) were comparable to those of 50μg RTS,S/AS01B in malaria-naïve adults at 28 days after final vaccination.

The 10μg dose induced more durable responses, with 2-fold higher NANP-specific IgG titres at 6 months compared with the 2μg and 50μg dose groups. R21 also boosted baseline humoral responses in Burkinabe adults with well-maintained responses suggesting natural boosting.

The R21/Matrix-M vaccine candidate is safe and has comparable immunogenicity to RTS,S/AS01B, even when administered at a five-fold lower 10μg dose in UK and African populations. This forms the basis for efficacy testing of this vaccine which could prove to be particularly cost-effective to manufacture and deploy.