The U.S. appears to be on the cusp of its first COVID-19 vaccine, as an independent panel of infectious disease experts, doctors and scientists met Thursday to decide whether the first candidate should be considered safe and effective.
A favorable vote on the Pfizer vaccine by the independent group, called the Vaccines and Related Biological Products Advisory Committee, would pave the way for an official green light from the U.S. government, which in turn would trigger the first shipment of 2.9 million doses to 636 sites across the country.
The Food and Drug Administration has not said when it will ultimately decide when and if to authorize the vaccine, but said it was working quickly to make that decision.
"We can act quickly, and we intend to. We understand the urgency of the situation," Stephen Hahn, commissioner of the Food and Drug Administration, told ABC's "Good Morning America" on Thursday.
"Again, there may be issues, medical, scientific issues we have to address after the discussion, and we will do so," he added. "We want to make sure we make the absolute best decision for the American people."
So far, all signs are favorable for the vaccine, which is already being distributed in the U.K. Canada also has authorized the vaccine.
An internal assessment released this week by the Food and Drug Administration already concluded the vaccine was remarkably effective with no known serious risks, although members were expected to ask questions Thursday about whether the vaccine could trigger an allergic reaction in some people.
"I did not see any examples of corners being cut," said Dr. Ofer Levy, a temporary voting member of the advisory committee and director of the Precision Vaccines Program at Harvard Medical School.
"I see the typical safety information one would expect," Levy said Wednesday ahead of the advisory committee meeting.
Hospitalizations and death numbers are soaring too, with fears in many cities that medical facilities are overwhelmed.
But some critical questions remain, including whether enough Americans will trust the vaccine to take it.
In a bid for transparency to bolster trust in the process, the FDA is livestreaming Thursday's meeting on its site, as well as social media platforms like YouTube and Twitter, so that the public can listen to outside experts, Pfizer and government scientists review the findings of a clinical trial that involved 44,000 people.
Levy said the transparency is critical.
"I believe if we let the process play out in this transparent way as designed by FDA, we will do justice to this product and to its potential to help the people of this country and hopefully around the world," Levy said.
If all goes well, administration officials predict the FDA would render its decision in days, possibly before next Tuesday. Within 24 hours of an FDA authorization, distribution of the 2.9 million doses would begin with another 2.9 million close behind and 500,000 doses held in reserve.
Each person requires two doses of the Pfizer vaccine, which is estimated to be 95% effective.
Those initial shipments will cover just a fraction of the two groups designated first in line -- front-line health care workers and residents of long-term care facilities. Governors will decide which hospitals or pharmacies get the first doses.
"Hopefully, we will start impacting people's lives very quickly after the onset of the campaigns to immunize," said Moncef Slaoui, Trump's chief scientific advisor on vaccines.
Slaoui also told reporters on Wednesday that he suspects regulators will ultimately advise people with a history of severe allergic reactions not to take the vaccine following reports of two allergic reactions in the U.K.
"My expectation is that this is new news," he said of the allergic reactions. And "the expectation would be that subjects with known severe reaction -- allergic reaction -- should not take the vaccine, until we understand exactly what happened here."
Dr. Anthony Fauci, the nation's top infectious disease expert, said Wednesday that it's possible people will wind up excluded from receiving a particular type of vaccine, but noted there are multiple candidates in the mix.
"If in fact, we do find out that there is a consistent issue of certain subset of people like those with allergic reactions, you'll always have other vaccine platforms that you can use," he said at an event hosted by the Harvard T.H. Chan School of Public Health.
Moderna also has applied for FDA authorization of its vaccine. Slaoui said those details will be published in a few days and that "the data are impressive and compelling."
The U.S. is counting on the Moderna vaccine to come through to hopefully vaccinate 20 million Americans by the end of the year, increasing to 50 million total by the end of January.
"We feel very confident that by late March, early April, the rest of the population -- those beyond the health care workers, those beyond the elderly -- will be able to receive their vaccines as well," Lt. Gen. Paul Ostrowski, director of supply, production and distribution for Operation Warp Speed, told ABC's "Good Morning America."
ABC News' Arielle Mitropoulos, Eric Strauss, Sony Salzman and Stephanie Ebbs contributed to this report.
This report was featured in the Thursday, Dec. 10, 2020, episode of “Start Here,” ABC News’ daily news podcast.
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