A Covid-19 Vaccine developed by Oxford University is been tried on humans in South Africa and Brazil.
About 2,000 people in South Africa will be involved in what is widely considered to be one of the earliest and most advanced trials for a vaccine to tackle the pandemic.
The first doses of the vaccine are being administered in Johannesburg.
South Africa has been chosen, not just for its expertise in this field, but because Covid-19 is spreading fast in the country.
It therefore makes easier for scientists to find a community at immediate risk of infection, and to confirm whether the vaccine is effective.
Similar tests are already underway in the UK, although the infection rate has slowed, hence the move, not just to South Africa, but also Brazil, where 5,000 people will be involved in the trial.