A health worker prepares a dose of the Pfizer coronavirus vaccine at the newly-opened mass vaccination program for the elderly at a drive-thru vaccination center outside Johannesburg, South Africa, Tuesday, May 25, 2021. South Africa aims to vaccinate 5 million of its older citizens by the end of June. (AP Photo/Themba Hadebe)

A health worker vaccinates a retiree with a the first dose of the Pfizer coronavirus vaccine inside a tent, during a mass vaccination program for the elderly at the clinic outside Johannesburg, South Africa, Monday, May 24, 2021. South Africa aims to vaccinate 5 million of its older citizens by the end of June. (AP Photo/Themba Hadebe)

Retirees wait to receives a first dose of the Pfizer coronavirus vaccine in a tent during a mass vaccination program for the elderly at the clinic outside Johannesburg, South Africa, Monday, May 24, 2021. South Africa is in a race against time to vaccinate as many people as possible with signs the virus may be surging again. (AP Photo/Themba Hadebe)

A retiree receives the first dose of the Pfizer coronavirus vaccine from a health worker inside a tent, during a mass vaccination program for the elderly at the clinic outside Johannesburg, South Africa, Monday, May 24, 2021. South Africa is in a race against time to vaccinate as many people as possible with signs the virus may be surging again. (AP Photo/Themba Hadebe)