"Today, I'm calling on more countries -- more companies, I should say -- in the private sector to step up with vaccine requirements that will reach millions more people," Biden said. "If you're a business leader, a nonprofit leader, a state or local leader, who has been waiting for full FDA approval to require vaccinations, I call on you now to do that, require it."
The full approval will likely give legal cover to many organizations who want to require vaccinations for their employees as the delta variant surges nationwide. The U.S. has so far vaccinated 71% of the eligible population, but under-vaccinated areas like the Southeast have proven that the virus will continue to spread wherever there is not ample protection.
"Let me say this loudly and clearly, if you're one of the millions of Americans who said that they will not get the shot until it has full and final approval of the FDA, it's now happened," Biden said during remarks at the White House. "The moment you've been waiting for is here."
It indicates that Pfizer has shown enough effectiveness and safety data to meet the stringent Biologics License Application (BLA) requirements, which includes at least six months of safety data from a majority of the volunteers in a large, final stage clinical trial.
"Based on the longer-term follow-up data that we submitted, today's approval for those aged 16 and over affirms the efficacy and safety profile of our vaccine at a time when it is urgently needed," Albert Bourla, Pfizer CEO said in a statement to ABC News. "Hundreds of millions of doses of our vaccine already have been administered in the U.S. since December 2020, and we look forward to continuing to work with the U.S. government to reach more Americans."
This prioritized review entailed government scientists pouring over hundreds of thousands of pages of safety and efficacy data at a rapid-fire pace, conducting meticulous inspections of Pfizer's manufacturing process.
"This is a pivotal moment for our country in the fight against the pandemic," acting FDA Commissioner Janet Woodcock said in a briefing with reporters after announcing the full approval.
"Working around the clock, FDA staff were able to complete the evaluation of this biologics license application in just over three months," Woodcock said. "This is an unprecedented timeline given the volume of review and the meticulous manner in which it was done, but we want to underscore that our efforts to move as quickly as possible have in no way sacrifice scientific standards for the integrity of our process."
As Biden said in his speech, there will be increasing pressure for Pfizer's full and formal approval to pave the way for further vaccine mandates in both the public and private sector, akin to existing vaccine mandates for other FDA-approved vaccines. Some businesses and state leaders have held off thus far, signaling they'd wait for full approval before imposing tighter requirements.
At a press conference on Capitol Hill Monday, however, several Republicans pushed back on vaccine mandates.
Rep. Chip Roy, R-Texas, a cancer survivor, touted the vaccine but said it should be up to Americans and their doctors to decide whether they should get vaccinated and Rep. Bob Good, R-Va., also attacked the Biden administration for requiring the vaccine in the military.
"What we shouldn't do is mandate anyone to get the vaccine and certainly not our military," he said.
Federal, state and local health officials have expressed optimism that full approval will help dissolve some of the lingering hesitancy around taking a shot when it was only authorized for emergency use -- a forecast recent polling has also reflected.
Similar to the president, Dr. Peter Marks, director of the Center for Biologics Evaluation and Research and overseer of the approval process, urged people who were waiting for this moment to get vaccinated to do so.
"By following our rigorous processes to evaluate this application, we hope those who have waited until now to make the choice to protect themselves and thereby also help protect their communities by reducing the spread of COVID-19, will go and get vaccinated," Marks said in Monday's briefing with reporters alongside Woodcock.
Marks said the agency worked "tirelessly" around the clock to approve the vaccine in such a short time frame. The whole process took about half the time it would under normal circumstances, Marks said -- though the FDA was under pressure in recent weeks to move faster because more people might use full approval as a reason to get vaccinated.
"People have been wondering what took so long. Well, FDA, when we conduct a review of biologics license application, we are highly rigorous in what we do and we don't just look at what the summaries of data are -- we go down to the level of the individual patients," Marks said.
In this case, that meant 20,000 patients who received a vaccine and 20,000 who received a placebo. The FDA visited the clinical trials sites, inspected the vaccine manufacturers and combed through thousands of pages of patient data to do its own analyses, as well as do risk-benefit analysis on data that emerged after the clinical trials were over, when hundreds of millions of people got the shot.
"We reviewed hundreds of thousands of pages of data and information about the vaccine safety, effectiveness, and manufacturing quality, and we concluded and conducted inspections of various facilities for the vaccine manufacturer," Marks said.
The team "worked night and day to get this done," he said.
Former acting CDC Director Dr. Rich Besser, president of the Robert Wood Johnson Foundation, said the timing "could not come at a more important time, as the highly contagious Delta variant continues to drive up caseloads and deaths across the U.S."
"I am hopeful that full approval will address any remaining concerns and will move many people to a 'yes' on vaccination," Besser said in an interview with ABC News.
Pfizer was the first to request full approval in the U.S.; other COVID vaccine makers are likely to follow suit. All three authorized vaccines were granted emergency authorization based on massive clinical trials involving tens of thousands of volunteers.
Federal health officials have come under immense political pressure from all sides to get the approval done as soon as possible -- as much of the country faces yet another surge, and the delta variant threatens hard-fought wins in the fight against the virus.
In private calls with the White House COVID, team obtained by ABC News, some of nation's governors have recently expressed waning patience and frustration over the wait for full approval of the vaccine -- saying the FDA either needs to act or be transparent about how much longer there is to wait -- given that the lack of full approval was a recurring reason they had heard from the hesitant over their not taking the shot yet.
The FDA had made clear getting Pfizer's vaccine to the approval finish line was a top priority, with an "all-hands-on-deck approach" and "moving forward as rapidly as possible."
ABC News learned in late July the agency would reprioritize some of its personnel and technology resources from "across the agency" and reshuffling other existing work, in order to finish the review faster, devoting those additional resources towards expediting the process for Pfizer's approval.
"We recognize that for some, the FDA approval of COVID-19 vaccines may bring additional confidence and encourage them to get vaccinated," an agency spokesperson told ABC in late July, promising any approved vaccine would meet "rigorous standards for safety, effectiveness, and quality."
ABC News' Cheyenne Haslett, Ben Gittleson, Justin Gomez, Benjamin Siegel and Briana Stewart contributed to this report.