Robyn Porteous, a vaccine trials' volunteer, is injected with a vaccine as part of the country's human clinical trial for potential vaccines after being tested for the coronavirus disease (COVID-19), at the Wits RHI Shandukani Research Centre in Johannesburg, South Africa, August 27, 2020. South African volunteers on AstraZeneca's experimental coronavirus vaccine trial said they were not worried to hear the trial had been paused after a participant fell ill and they hoped to be part of a potential solution to the pandemic. REUTERS/Siphiwe Sibeko

Robyn Porteous, a vaccine trials' volunteer, is tested for the coronavirus disease (COVID-19) before being injected with a vaccine as part of the country's human clinical trial for potential vaccines at the Wits RHI Shandukani Research Centre in Johannesburg, South Africa, August 27, 2020. Some 2,000 volunteers in South Africa are taking part in the trial which was paused globally on Tuesday after an unexplained illness in a participant. An independent committee will review safety data. REUTERS/Siphiwe Sibeko

A syringe with a vaccine is seen ahead of trials by volunteers testing for the coronavirus disease (COVID-19), and taking part in the country's human clinical trial for potential vaccines at the Wits RHI Shandukani Research Centre in Johannesburg, South Africa, August 27, 2020. The vaccine, developed with the University of Oxford, has been described by the World Health Organization as probably the world's leading candidate and the most advanced in terms of development. REUTERS/Siphiwe Sibeko

A health worker talks to a vaccine trials' volunteer before he is tested for the coronavirus disease (COVID-19) and takes part of the country's human clinical trial for potential vaccines at the Wits RHI Shandukani Research Centre in Johannesburg, South Africa, August 27, 2020. REUTERS/Siphiwe Sibeko

A health worker looks on as a vaccine trials' volunteer arrives before testing for the coronavirus disease (COVID-19), and taking part in the country's human clinical trial for potential vaccines at the Wits RHI Shandukani Research Centre in Johannesburg, South Africa, August 27, 2020. REUTERS/Siphiwe Sibeko

Vaccine trials' volunteers wait for their names to be called before testing for the coronavirus disease (COVID-19), and taking part of the country's human clinical trial for potential vaccines at the Wits RHI Shandukani Research Centre in Johannesburg, South Africa, August 27, 2020. REUTERS/Siphiwe Sibeko