[2nd UPDATE ] The United States Food and Drug Administration said it authorized the use of Pfizer Inc's COVID-19 vaccine on Friday, with the first inoculations expected within 24 hours, marking a turning point in the United States where the pandemic has killed more than 292,000 people.
President Donald Trump said late on Friday that the first shot would be administered in less than 24 hours.
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The vaccine, developed with German partner BioNTech, was shown to be 95% effective in preventing the disease in a late-stage trial.
The FDA said the vaccine can be given to people aged 16 and older. Health care workers and elderly people in long-term care facilities are expected to be the main recipients of a first round of 2.9 million doses.
The U.S. government has said it would begin distributing the vaccine around the country immediately after FDA authorization, and that the first inoculations would happen early next week.
Millions of Americans could begin getting vaccinated this month, especially if a second vaccine from Moderna Inc is quickly approved.
The Pfizer/BioNTech vaccine was first approved in Britain earlier this month, and UK residents began receiving the shots on Tuesday. Canada also authorized the vaccine and expects to start inoculations next week.
Mexico and Bahrain have also approved the vaccine.
The FDA authorization comes at a time when infections, hospitalizations and deaths are soaring to record levels in the United States, which has failed to mount a coordinated effort to slow the spread of the virus. Earlier this week, the one-day COVID-19 death total topped 3,000, while hospital intensive care units across the country are nearing capacity, threatening to overwhelm health care systems.
Others with vaccines in advanced development include Moderna, which could win emergency US authorization as soon as next week, AstraZeneca Plc with Oxford University, and Johnson & Johnson.
BioNTech began developing the vaccine in January, using a technology called synthetic messenger RNA (mRNA) that had yet to produce an approved product. The technology uses a chemical messenger to instruct cells to make proteins that mimic part of the new coronavirus, which the immune system learns to recognize as an invader. BioNTech struck a development deal with Pfizer in March.
The vaccine comes with complex distribution challenges as it must be shipped and stored at -70 Celsius (-94 F), requiring specialized ultra-cold freezers or supplies of dry ice.
Moderna's vaccine employs the same technology but does not need to be stored at sub-Arctic temperatures.
THE FIRST SHOTS
Pfizer has developed a special shipping container that will be filled with dry ice to keep the vaccine from spoiling. Many states are concerned about whether there is enough dry ice for shipments to rural areas that lack the specialized freezers, but Pfizer believes there should be sufficient supply.
The US quest for a vaccine has been the central response to the pandemic from a Trump administration that has mostly otherwise left states to fend for themselves. It has said it will have enough to supply all of the 330 million U.S. residents who wish to be vaccinated by the middle of 2021.
The government has ordered 100 million doses of the Pfizer vaccine - enough to inoculate 50 million people - through its Operation Warp Speed virus development program and could negotiate for more. The status of those talks are unclear.
Pfizer board member and former FDA commissioner Scott Gottlieb said in an interview with CNBC earlier this week that the company had offered to sell the United States more doses as recently as last month but had been turned down.
The United States has agreed to buy 200 million doses of Moderna's two-dose vaccine. The government also has supply deals with J&J and AstraZeneca, but authorization of those vaccines are not imminent.
Top U.S. infectious diseases expert Dr. Anthony Fauci said if distribution goes well and enough Americans agree to get vaccinated, relief for a pandemic weary nation may be on the horizon.
"If we do it efficiently enough by the second quarter of 2021, and by the end of summer or end of third quarter, we may actually have enough herd immunity protecting our society," he said. "And as we get to the end of 2021, we could approach very much some degree of normality that is close to where we were before."