The Volunteer Information Sheet (VIS) will contain detailed information about the study and will be distributed to the proposed volunteers. The investigators will endeavour to ensure that all volunteers fully understand the risks. Any volunteer who appears to have less than complete understanding will be considered unable to give consent. If unable to sign, the volunteer will be asked to thumbprint the consent form in the presence of an impartial witness who will be present during the screening procedures and will countersign the consent form. Fully consented volunteers will undergo the full screening procedures. This consists of medical history, physical examination, and blood sampling for screening tests.