Putseltso Lesofe, gives a patient a COVID-19 test at the Ndlovu clinic in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. The Ndlovu center is running a study of the Johnson & Johnson COVID-19 vaccine with 602 people from the community participating. (AP Photo/Jerome Delay)

Nurse Asnath Masango, 56, waits for a patient at Ndlovu Care Group in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. The Ndlovu center is running a study of the Johnson & Johnson COVID-19 vaccine with 602 people from the community participating. Masango said she can't wait to get vaccinated. (AP Photo/Jerome Delay)

Dr. Rebone Maboa, right, meets with staff at Ndlovu Care Group in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. Maboa, who recently recovered from COVID-19, is running a study of the Johnson & Johnson vaccine at the center, with 602 people from the community participating. (AP Photo/Jerome Delay)

Patients taking part in a study of the Johnson & Johnson COVID-19 vaccine wait outside at the Ndlovu Care Group in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 202. 602 people from the community participating in the study. (AP Photo/Jerome Delay)

Blood samples from people participating in a COVID-19 vaccine study are processed at the Ndlovu Care Group in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. the Ndlovu group is running a study of the Johnson & Johnson vaccine with 602 people from the community participating. (AP Photo/Jerome Delay)

Puseletso Lesofe works on blood samples from people participating in a COVID-19 vaccine study at the Ndlovu Care Group in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. the Ndlovu group is running a study of the Johnson & Johnson vaccine with 602 people from the community participating. (AP Photo/Jerome Delay)

Putseltso Lesofe, right, and Carol Ditshego, left, brief a patient before giving her a COVID-19 test at the Ndlovu clinic in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. The Ndlovu center is running a study of the Johnson & Johnson COVID-19 vaccine with 602 people from the community participating. (AP Photo/Jerome Delay)

Carol Ditshego waits for patients coming for a COVID-19 test at the Ndlovu clinic in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. The Ndlovu center is running a study of the Johnson & Johnson COVID-19 vaccine with 602 people from the community participating. (AP Photo/Jerome Delay)

CJ Umunnakw, a virologist, works in the lab at the Ndlovu Care Group in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. Ndlovu is running a study of the COVID-19 Johnson & Johnson vaccine with 602 people from the community participating. (AP Photo/Jerome Delay)

A thermometer display reads minus 83 degrees Celsius on a medical storage fridge at the Ndlovu clinic's lab in Elandsdoorn , 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. The clinic is conducting a study of the Johnson & Johnson COVID-19 vaccine with 602 people from the community participating. (AP Photo/Jerome Delay)

Patients walk through the hallways of the Ndlovu clinic in Elandsdoorn, 200 kms north-east of Johannesburg Thursday Feb. 11, 2021. The Ndlovu center is running a study of the Johnson & Johnson COVID-19 vaccine with 602 people from the community participating. (AP Photo/Jerome Delay)