The Food and Drug Administration on Friday said it had authorized the first Covid-19 vaccine for emergency use in the United States — the first major, tantalizing indication for Americans that the pandemic's days may be numbered.
A letter from the FDA to Pfizer reads that "the known and potential benefits of Pfizer-BioNTech COVID‑19 vaccine" outweigh its potential risks for people ages 16 and older.
"It's nothing short of a medical miracle to have FDA authorization of a vaccine for Covid-19 just over 11 months since the virus was made known to the world," Health and Human Services Secretary Alex Azar said in a statement Friday night.
FDA commissioner Dr. Stephen Hahn in a statement called the authorization "a significant milestone in battling this devastating pandemic that has affected so many families in the United States and around the world."
The vaccine, made by Pfizer and its partner BioNTech, is expected to be shipped nationwide as soon as this weekend, earmarked for front-line health care workers, as well as staff working at long-term care facilities.
Those two groups in Phase 1 of the vaccine rollout together represent around 24 million people — 3 million residents of long-term care facilities and 21 million health care workers on the front lines of treating Covid-19 patients.
"Our teams are engaged and ready to receive it," said Onisis Stefas, chief pharmacy officer for Northwell Health in New York, adding that health systems should get about 48 hours notice before shipment.
With the FDA's authorization, shipments of the vaccine are expected to move quickly, so that the first vaccine doses could be administered Monday or Tuesday, an official at HHS confirmed to NBC News on Friday.
Pfizer's Covid-19 vaccine has been shown to be both safe and highly effective. Phase 3 clinical trials of the vaccine reveal the shot is 95 percent effective across a variety of age and racial groups and ethnicities when given in two doses, about three weeks apart.
Documents released Tuesday revealed that even just one shot may offer about 50 percent immunity, though the FDA said two shots are necessary for maximum protection.
On Thursday, a group of independent advisers to the FDA overwhelmingly voted in favor of the emergency use authorization by the regulatory agency. The FDA predictably followed its panel's advice, authorizing the vaccine the next day.
There were a handful of dissenters among the advisory panel, however, some of whom said there is not enough data to recommend the shots for teens 16 and 17, although there were participants of that age in the clinical trials.
One of those members who voted against advising emergency use was Dr. Archana Chatterjee, dean of the Chicago Medical School and vice president for medical affairs at Rosalind Franklin University in Chicago.
"We have limited safety and efficacy data on how the vaccine affects the pediatric population," Chatterjee wrote in an email to CNBC. "Since most of them will not be eligible to receive the vaccine in the near future, and because they are not in a high-risk group, I believe we have time to gather and analyze additional data in this and younger age groups."
Otherwise, Chatterjee said, she supported the emergency use authorization for the Pfizer vaccine.
Another member who voted no, Dr. David Kim, director of the vaccines division of the Office of Infectious Disease and HIV/AIDS Policy in the Department of Health and Human Services, told CNBC in an email that he would have voted yes "most enthusiastically" had the vote been limited to recommending authorization to those ages 18 and older.
In the end, the FDA determined that the data supported the vaccine's use in millions of people 16 years of age and older, including healthy individuals.
As of yet, there is no indication those who've had Covid-19 should not get the vaccine. Covid-19 reinfections are thought to be rare, but if natural antibody levels wane over time, it may be possible for a person to become infected more than once.
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The U.S. will be the fourth country to roll out the Pfizer vaccine, after the United Kingdom, Canada and Bahrain.
Potential side effects of the vaccine will be monitored closely. Fever, fatigue, headache and muscle and joint pain may be expected.
"Adverse reactions are not always a bad thing," Stefas of Northwell Health, said. "It shows that your body is reacting to the vaccine, and that your immune response is working."
Earlier this week, two health care workers in the U.K. experienced serious allergic reactions almost immediately after receiving the Pfizer vaccine, prompting British regulators to warn that people with a history of severe allergic reactions shouldn't receive the vaccine. In the FDA guidance, the agency said that the vaccine should not be given to individuals with "known history of severe allergic reaction" or anaphylaxis.
The FDA also cautioned that medical treatment for allergic reactions should be given immediately if an individual experiences an anaphylactic reaction following the Pfizer vaccine.
The FDA advisory panel is scheduled to meet again virtually December 17 to consider a similar vaccine, made by Moderna. In November, the company released preliminary results from its Phase 3 trial, which showed that the vaccine is nearly 95 percent at preventing symptomatic illness.
More details from Moderna are expected to be released publicly before next week's meeting.