A man carries his empty oxygen tank to be filled after arriving at the head of the line, in the Villa El Salvador neighborhood of Lima, early Thursday morning, Feb. 18, 2021. A crisis over the supply of medical oxygen for coronavirus patients has struck in Africa and Latin America, where warnings went unheeded at the start of the pandemic and doctors say the shortage has led to unnecessary deaths. (AP Photo/Martin Mejia)

Cars line up in a parking lot at NRG Park as people wait to receive a COVID-19 vaccine at a federally supported supersite at the Harris County facility, Wednesday, Feb. 24, 2021, in Houston. ( Mark Mulligan/Houston Chronicle via AP)

FILE - This Dec. 2, 2020 photo provided by Johnson & Johnson shows vials of the Janssen COVID-19 vaccine in the United States. Johnson & Johnson’s single-dose vaccine protects against COVID-19, according to an analysis by U.S. regulators Wednesday, Feb. 24, 2021, that sets the stage for a final decision on a new and easier-to-use shot to help tame the pandemic. The Food and Drug Administration’s scientists confirmed that overall, it's about 66% effective and also said J&J's shot, one that could help speed vaccinations by requiring just one dose instead of two, is safe to use. (Johnson & Johnson via AP)

Senior citizens wait under an orange tent to be inoculated with a dose of the Russian COVID-19 vaccine Sputnik V, at the Sports Center in the Xochimilco borough of Mexico City, Wednesday, Feb. 24, 2021. (AP Photo/Marco Ugarte)

Residents of the Iztacalco borough follow a long, snaking line to receive doses of the Russian COVID-19 vaccine Sputnik V, during a mass vaccination campaign for Mexicans over age 60, at the Advanced School for Physical Education, in Mexico City, Wednesday, Feb. 24, 2021. (AP Photo/Rebecca Blackwell)

Students hold signs as they take part in a rally to encourage wider opening of in-person learning in the Issaquah School District, Wednesday, Feb. 24, 2021, in Issaquah, Wash., east of Seattle. Students in kindergarten and lower-elementary grades in the district recently returned to school under a hybrid in-person learning program, but older elementary, middle-, and high school students are still being taught remotely. (AP Photo/Ted S. Warren)

FILE - In this Feb. 16, 2021, file photo, motorists wait to get their COVID-19 vaccine at a federally-run vaccination site set up on the campus of California State University of Los Angeles, in Los Angeles. California is revamping a plan to help essential workers and seniors in underserved communities get coronavirus vaccinations after officials learned appointment access codes were leaked to people not eligible for the shots. The move comes as the state of 40 million people is striving to prioritize vaccinating the most vulnerable. (AP Photo/Jae C. Hong, File)

A solitary runner passes under the flags hanging at half-staff surrounding the Washington Monument at day break in Washington, Wednesday, Feb. 24, 2021. President Joe Biden ordered the flags to be lowered in honor of the 500,000 lives lost to COVID-19 in the U.S. (AP Photo/J. David Ake)

A medical worker injects a man with a dose of the Russian COVID-19 vaccine Sputnik V at the Palacio de los Deportes, in the Iztacalco borough of Mexico City, Wednesday, Feb. 24, 2021. (AP Photo/Rebecca Blackwell)

A medical worker injects a woman with a dose of the Russian COVID-19 vaccine Sputnik V at the Palacio de los Deportes, in the Iztacalco borough of Mexico City, Wednesday, Feb. 24, 2021. (AP Photo/Rebecca Blackwell)

A medical worker injects a woman with a dose of the Russian COVID-19 vaccine Sputnik V at the Palacio de los Deportes, in the Iztacalco borough of Mexico City, Wednesday, Feb. 24, 2021. (AP Photo/Rebecca Blackwell)

A medical worker injects a woman with a dose of the Russian COVID-19 vaccine Sputnik V at the Palacio de los Deportes, in the Iztacalco borough of Mexico City, Wednesday, Feb. 24, 2021. (AP Photo/Rebecca Blackwell)

A patient with coronavirus breathes with the help of an oxygen mask at an intensive care unit in the regional hospital in Chernivtsi, western Ukraine, Wednesday, Feb. 24, 2021. The number of coronavirus cases in the western part of the country has risen sharply since the end of a strict two-week lockdown last month. (AP Photo/Evgeniy Maloletka)

An elderly woman is injected with a dose of China's Sinovac Biotech CoronaVac vaccine for COVID-19 at the Jose Joaquin Vargas Special Women's Center in Sibate, Colombia, Wednesday, Feb. 24, 2021. The geriatric center specializing in treating psychiatric patients began vaccinating patients over 80 against the new coronavirus. (AP Photo/Fernando Vergara)

A homeless man begs for alms at a busy intersection in Johannesburg, Wednesday, Feb. 24, 2021. In Finance Minister's budget speech in Parliament, Tito Mboweni said the COVID-19 vaccination drive in the country will help South Africa's economy, the most developed in sub-Saharan Africa, to rebound by 3.4% this year after a statistics agency said the country's unemployment rate reached 32.5%. (AP Photo/Denis Farrell)