The nation's most populous state says it's pivoting fast following a chaotic and inefficient county-based rollout of the vaccine. Surgeon General Dr. Nadine Burke Harris tells NPR about the do-over.

Gov. Ron DeSantis is touting the success of his policy providing COVID-19 vaccines to everyone 65 years and older in the state. But critics say the vaccine distribution favors some groups over others.

Nigerian physician Ifeanyi Nsofor writes: "I was elated when the first COVID-19 vaccine was shown to be effective. ...My joy was cut short when richer Western nations began buying up the vaccine doses."

Georgia residents age 65 and up can now schedule appointments to get a COVID-19 vaccine, but actually getting one could be a challenge. That may change in the coming weeks as President Joe Biden's administration is working to purchase an additional 200 million doses of the two COVID-19 vaccines that have been authorized for emergency use, with the goal, the White House says, of having enough vaccine supply for nearly the entire U.S. population by the end of the summer.

"The companies must deliver. They must honor their obligations," the European Commission's president said after both AstraZeneca and Pfizer said they were experiencing shipping issues.

In 1957, residents of the southwestern town Protection set an example by being the first in the U.S. to be fully inoculated against polio. Now locals are divided on the safety of COVID-19 vaccines.

The two companies making COVID-19 vaccines each promised to deliver 100 million doses to the federal government by the end of March. So far, they appear to be running behind.

As the rollout of COVID-19 vaccines unfolds in the U.S., numerous questions around distribution, supply, hesitancy and efficacy persist. Experts from Harvard and the CDC tackle these questions.

Ellen Johnson Sirleaf, a Nobel Peace Prize recipient and former president of Liberia, says much of Africa may be left out until 2022. "We don't have the resources. It's as simple as that," she says.

Grocers from Aldi to Trader Joe's are pitching financial incentives to their employees to encourage them to get vaccinated.

For two of the biggest obstacles to curbing the pandemic, it won't just be federal officials who will lead the way, says Dr. Celine Gounder, a member of President Biden's COVID-19 advisory board.

Local health departments and pharmacies are distributing COVID-19 vaccines as fast as possible. But appointment hotlines are overwhelmed, making it tough to schedule a first dose, let alone a second.

Research suggests the vaccine prevents disease only 50% of the time. But it could still have a big impact. And many countries are betting on it.

First, can someone who has been vaccinated still spread the disease? Second, will the vaccine remain effective as the virus itself evolves? And third, how long will the vaccine's protection last?

Emergent BioSolutions is under contract with Operation Warp Speed to make COVID-19 vaccines, but the terms could allow employees and their families to get vaccinated ahead of schedule.