• The FDA said data from Pfizer's coronavirus vaccine trials was "consistent" with recommendations put forth by the agency for an emergency use authorization.
• FDA staff also said data submitted appeared to show the vaccine provided protection after the first dose.
• It added that two doses of the vaccine were "highly effective" in preventing confirmed cases of Covid-19.

The Food and Drug Administration said Tuesday that data from Pfizer's coronavirus vaccine trials was consistent with recommendations put forth by the agency for an emergency use authorization. It also said the vaccine was highly effective and did not raise any specific safety concerns.

In documents published ahead of an advisory meeting Thursday to review Pfizer's vaccine, FDA staff also said data submitted appeared to show the vaccine was at least 52% effective before the second dose and 82% effective for the combined group of people who took one or two doses.

Pfizer's vaccine recommends two doses about three weeks apart. The agency added that two doses of the vaccine were "highly effective" in preventing confirmed cases of Covid-19 at least seven days following the second dose. In such instances, the vaccine was 94.8% effective after seven days of the inoculation.

The FDA has indicated it would authorize a vaccine that's safe and at least 50% effective. The flu vaccine, by comparison, generally reduces people's risk of getting influenza by 40% to 60% compared with people who aren't inoculated, according to the CDC.

"As such, FDA has determined that the Sponsor has provided adequate information to ensure the vaccine's quality and consistency for authorization of the product under an EUA," the agency said on its website.

The FDA is expected to decide on whether to authorize Pfizer's vaccine within days. The U.K. on Tuesday began mass inoculations with the vaccine based on its approval of emergency use.

The documents posted Tuesday offer a glimpse of the FDA's view of the vaccine. The agency is scheduled to convene a meeting of its Vaccines and Related Biological Products Advisory Committee, a group of outside medical experts, on Thursday to review Pfizer's Covid-19 vaccine with German drugmaker BioNTech for emergency use.

Emergency use authorization means the FDA will allow some people to receive the vaccine as the agency continues to evaluate data. It isn't the same as a full approval, which can typically take months. The FDA granted emergency clearance for Gilead Sciences' remdesivir in May before giving full approval in late October.

If Thursday's meeting goes well and the advisory committee formally recommends the vaccine, the FDA could announce its authorization "within days," Health and Human Services Secretary Alex Azar told ABC News' "This Week" on Sunday. "But it's going to go according to FDA's gold-standard process, and I'm going to make sure it does," he added.

The FDA doesn't have to follow the advisory committee's recommendation, but the agency often does. Additionally, the FDA's positive assessment of the vaccine does not mean the committee will take the same stance at its meeting Thursday.

Pfizer submitted its Covid vaccine data to the FDA on Nov. 20. The company said a final analysis of its phase three clinical trial, with more than 43,000 participants, found the vaccine was 95% effective in preventing Covid, was safe and appeared to fend off severe disease. Its vaccine uses messenger RNA, or mRNA, technology. It's a new approach to vaccines that uses genetic material to provoke an immune response.

An authorization of the vaccine would be a pivotal moment in the pandemic, as public health officials say the U.S. is likely to face its worst public health crisis in history this winter. Hospitals across the U.S. already have a higher load of Covid patients than ever, and the country's outbreak is primed to set even more grim records this week. 

U.S. officials say they will distribute the vaccine within 24 hours of authorization. Initial doses of the vaccine will be limited as manufacturing ramps up, with top U.S. health officials predicting it will take months to immunize everyone who wants to be vaccinated against Covid in the U.S. The vaccine will likely be distributed in phases, with the Centers for Disease Control and Prevention prioritizing health-care workers and nursing homes.

There is currently insufficient data to make conclusions about the safety of the vaccine in children under age 16, pregnant women and people with compromised immune systems, the FDA said Tuesday.

The agency also wrote that patients who have had Covid-19 may still be at risk of reinfection and could benefit from the vaccine. 

Clarification: The FDA says Pfizer's vaccine is at least 52% effective after the first dose but before the second treatment. The agency said the vaccine appears to be 82% effective for the combined group of people who took one or two doses.