Volunteers will be randomised to receive either three (3) doses of R21/ Matrix-M1 or placebo (normal saline) as control. Simple randomisation into the study groups will be done by an independent statistician based at the University of Oxford. A randomisation code list will be generated by the independent statistician and its use guided by a clear Standard Operating Procedure (SOP). Allocation concealment will be employed by use of opaque sealed envelopes. As this is a single-blind clinical trial design, the laboratory scientists will be blinded to vaccine allocation until the end of the study.