People wait in the stands to receive coronavirus vaccinations at the Kololo airstrip in Kampala, Uganda, Monday, May 31, 2021. As virus cases surge in the world's poorest countries, a sense of dread is growing among millions of the unvaccinated, especially those who toil in the informal, off-the-books economy, live hand-to-mouth and pay cash in health emergencies. (AP Photo/Nicholas Bamulanzeki)

A matatu, or public minibus, displays an informational painting instructing people to wear masks to curb the spread of the coronavirus, in the low-income Kibera neighborhood of Nairobi, Kenya, Saturday, June 12, 2021. Africa has recorded more than 5 million confirmed COVID-19 cases, including 135,000 deaths. That is a small fraction of the world's caseload, but many fear the crisis could get much worse. ​(AP Photo/Brian Inganga)

A woman receives a coronavirus vaccination at the Kololo airstrip in Kampala, Uganda, Monday, May 31, 2021. Africa is especially vulnerable. As virus cases surge in the world's poorest countries, a sense of dread is growing among millions of the unvaccinated, especially those who toil in the informal, off-the-books economy, live hand-to-mouth and pay cash in health emergencies. (AP Photo/Nicholas Bamulanzeki)

Medical staff wearing protective equipment attend to patients affected by the COVID-19, at the Intensive Care Unit (ICU) of the Machakos County Level-5 hospital in Machakos, Kenya, Thursday June 17, 2021. Africa, whose 1.3 billion people account for 18% of the global population, has received only 2% of all vaccine doses administered globally. (AP Photo/Brian Inganga).

A man receives the Sinopharm COVID-19 vaccine at a vaccination center, in Kabul, Afghanistan, Wednesday, June 16, 2021. In Afghanistan, where a surge threatens to overwhelm a war-battered health system, 700,000 doses donated by China arrived over the weekend, and within hours, "people were fighting with each other to get to the front of the line," said Health Ministry spokesman Dr. Ghulam Dastigir Nazari. (AP Photo/Rahmat Gul)

FILE - In this June 5, 2021, file photo, a man carries goods at a street market in Port-au-Prince, Haiti. In Haiti, hospitals are turning away patients as the country awaits its first shipment of vaccines. A major delivery via COVAX was delayed amid government concern over side effects and a lack of infrastructure to keep the doses properly refrigerated. (AP Photo/Joseph Odelyn, File)

Medical staff wearing protective equipment attend to patients affected by the COVID-19, at the Intensive Care Unit (ICU) of the Machakos County Level-5 hospital in Machakos, Kenya, Thursday June 17, 2021. Africa, whose 1.3 billion people account for 18% of the global population, has received only 2% of all vaccine doses administered globally. (AP Photo/Brian Inganga).

A man receives the Sinopharm COVID-19 vaccine at a vaccination center, in Kabul, Afghanistan, Wednesday, June 16, 2021. In Afghanistan, where a surge threatens to overwhelm a war-battered health system, 700,000 doses donated by China arrived over the weekend, and within hours, "people were fighting with each other to get to the front of the line," said Health Ministry spokesman Dr. Ghulam Dastigir Nazari. (AP Photo/Rahmat Gul)

FILE - In this June 5, 2021, file photo, a hospital employee wearing protective gear transports oxygen tanks in Port-au-Prince, Haiti. In Haiti, hospitals are turning away patients as the country awaits its first shipment of vaccines. A major delivery via COVAX was delayed amid government concern over side effects and a lack of infrastructure to keep the doses properly refrigerated. (AP Photo/Joseph Odelyn, File)

Medical staff wearing protective equipment attend to patients affected by the COVID-19, at the Intensive Care Unit (ICU) of the Machakos County Level-5 hospital in Machakos, Kenya, Thursday June 17, 2021. Africa, whose 1.3 billion people account for 18% of the global population, has received only 2% of all vaccine doses administered globally. (AP Photo/Brian Inganga)

A boy steps across a flooded area next to an informational mural with words in Swahili advising people to protect themselves from the coronavirus and get vaccinated, in the low-income Kibera neighborhood of Nairobi, Kenya, Saturday, June 12, 2021. Africa's 1.3 billion people account for 18% of the world’s population. But the continent has received only 2% of all vaccine doses administered globally. (AP Photo/Brian Inganga)

A health worker administers a dose of the AstraZeneca vaccine at the sport park of Treichville in Abidjan, Ivory Coast, Wednesday, June 16, 2021. Africa's 1.3 billion people account for 18% of the world’s population. But the continent has received only 2% of all vaccine doses administered globally. (AP Photo/Leo Correa)

Residents, wearing face masks to help curb the spread of the coronavirus, line up to receive the Sinopharm COVID-19 vaccine at a vaccination center, in Kabul, Afghanistan, Wednesday, June 16, 2021. In Afghanistan, where a surge threatens to overwhelm a war-battered health system, 700,000 doses donated by China arrived over the weekend, and within hours, "people were fighting with each other to get to the front of the line," said Health Ministry spokesman Dr. Ghulam Dastigir Nazari. (AP Photo/Rahmat Gul)