FDA on Tuesday released its first scientific evaluation of Pfizer's and BioNTech's coronavirus vaccine candidate and confirmed the inoculation's effectiveness, paving the way for the agency to authorize the vaccine candidate's emergency use in the United States.

FDA scientists confirm the effectiveness of Pfizer's coronavirus vaccine candidate

FDA analyzed data submitted by Pfizer from its large-scale clinical trial on its coronavirus vaccine candidate. Pfizer began the clinical trial in July and recruited 44,000 study participants across Argentina, Brazil, and the United States. Half of the participants received two doses of the vaccine candidate three weeks apart, and the other half of the participants received a placebo. After receiving their shots, the participants went on with their normal lives and were potentially exposed to the novel coronavirus in their communities, the Washington Post reports.

Overall, FDA found that the data from the clinical trial showed Pfizer's vaccine candidate appears to be safe and effective at preventing Covid-19, the disease caused by the novel coronavirus, regardless of a person's age, race, weight, or underlying health conditions.

According to FDA's analysis, Pfizer's vaccine candidate appeared to provide partial protection against Covid-19 nearly two weeks after patients received their first dose of the vaccine. The agency found that, in the three weeks between a participant receiving their first and second doses of the experimental vaccine, the vaccine candidate appeared to be about 52% effective at preventing illness. However, FDA scientists noted that there isn't enough data to draw firm conclusions on the vaccine candidate's effectiveness with only one dose, the Post reports.

FDA scientists said Pfizer's vaccine candidate appears to provide patients with the greatest protection against illness after they've received their second dose. Specifically, the scientists found that Pfizer's vaccine candidate appeared to be 95% effective at preventing Covid-19 after participants received their second dose of the experimental inoculation. FDA scientists also found that protection against Covid-19 appeared to last for at least two months after participants had received their second dose of the vaccine candidate.

In addition, FDA scientists found that Pfizer's vaccine candidate has similar rates of effectiveness among people of different ages, genders, races, and weights. For example, the scientists found that the vaccine candidate worked well in obese people and people who are older than 65—which are two groups that have a comparatively higher risk of developing severe cases of Covid-19.

In terms of safety, FDA found that the vaccine candidate had not produced serious side effects among more than 37,000 participants who so far have been tracked for at least two months after they received their last dose of the experimental vaccine. According to the Associated Press, the two-month period after a patient receives a vaccine is typically when serious side effects would emerge.

The scientists found that the vaccine candidate's most-reported side effects were injection-site pain and flu-like reactions, which tended to last up to two days. According to the scientists, more than 50% of adults under the age of 55 reported experiencing fatigue or headache, 33% reported having chills or muscle pain, and 16% reported having a fever—but older adults were less likely to report experiencing those side effects. The scientists said many participants who received the experimental vaccine reported feeling those side effects in the hours after they received the second dose, suggesting that people may have to plan to rest and/or take a day off work after receiving the second dose, the New York Times reports.

FDA's scientists also noted that four participants who received Pfizer's vaccine candidate had developed a form of facial paralysis called Bell's palsy. However, the scientists said they did not suspect that the condition was linked to the experimental vaccine.

Many observers said FDA's analysis appears to bode well for the vaccine candidate, which the agency currently is reviewing for an emergency use authorization (EUA) in the United States.

"This is what an A+ report card looks like for a vaccine," said Akiko Iwasaki, an immunologist at Yale University.

"I found myself trembling reading this," said Gregory Poland, a vaccine researcher at the Mayo Clinic, referring to the robust response to the vaccine candidate among obese and older people. "This is a grand slam by any measure."

What happens next?

FDA released the scientific review ahead of a Thursday meeting where an FDA advisory panel will evaluate the vaccine candidate and determine whether there is enough evidence to support an EUA. FDA Commissioner Stephen Hahn in an interview with NPR said FDA will likely make a decision on whether to issue an EUA for the vaccine candidate "shortly after" that meeting.

"A lot of what this depends upon is what the discussion is like [with] these outside experts from the vaccine advisory committee," Hahn said. "If they have substantial questions or additional analyses that they think are relevant to our decision-making, we will judge whether that's important to do. That may need to be done and that may contribute to some additional time needed."

In addition, the Advisory Committee on Immunization Practices (ACIP), an independent panel that advises CDC on vaccines, will meet on Friday to review data on Pfizer's vaccine candidate and determine its recommendations for how the vaccine candidate should be distributed and administered if it's authorized for use in the United States. ACIP is expected to vote on those recommendations on Sunday, Reuters reports.

William Schaffner, an infectious disease expert and non-voting member of ACIP, said the gap between ACIP's two planned meetings—one on Friday and one on Sunday—will allow FDA the time to potentially issue an EUA for the vaccine candidate before ACIP's planned vote on its recommendations.

Review comes as America's coronavirus epidemic continues to surge

FDA's analysis of Pfizer's coronavirus vaccine candidate comes as U.S. officials on Tuesday reported about 220,225 new cases of the novel coronavirus, according to data compiled by the Times. As of Wednesday morning, U.S. officials had reported a total of about 15.2 million cases of the virus since America's epidemic began—up from about 15 million cases reported as of Tuesday morning.

According to the Times, the United States' average daily number of newly reported coronavirus cases over the past week was 207,064—which is up by 18% when compared with the average from two weeks ago.

As of Wednesday morning, data from the Times showed that the rates of newly reported coronavirus cases were "staying high" in Puerto Rico; the U.S. Virgin Islands; Washington, D.C.; and 41 states that have had a daily average of at least 15 newly reported cases per 100,000 people over the past week. Those states are Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Idaho, Illinois, Indiana, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Mississippi, Missouri, Nebraska, Nevada, New Hampshire, New Jersey, New York, North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, Tennessee, Texas, Utah, Vermont, Virginia, Washington, and West Virginia.

The Times' data also showed that, as of Wednesday morning, the daily average number of newly reported cases over the past seven days was "going down" in eight states that had been seeing comparatively higher rates of coronavirus transmission. Those states are Iowa, Minnesota, Montana, New Mexico, North Dakota, South Dakota, Wisconsin, and Wyoming.

In the Guam and Hawaii, meanwhile, rates of newly reported coronavirus cases were "staying low" as of Wednesday morning, according to the Times' analysis.

Meanwhile, U.S. hospitalizations for Covid-19 grew to a new high for the eleventh consecutive day on Tuesday, according to data from The Atlantic's COVID Tracking Project. The data shows that 104,600 Americans with Covid-19 were hospitalized for treatment on Tuesday, including 20,483 who were receiving care in an ICU and 7,245 who were on a ventilator.

U.S. officials on Tuesday also reported about 2,597 new deaths tied to the novel coronavirus. As of Wednesday morning, U.S. officials had reported a total of about 286,443 U.S. deaths linked to the virus since the country's epidemic began, up from about 283,835 deaths reported as of Tuesday morning.