In a major milestone, an advisory panel of the United States Food and Drug Administration on Friday approved with an overwhelming majority the emergency use authorisation of a Covid-19 vaccine developed by Pfizer and BioNTech, reported Reuters.

The FDA is expected to authorise emergency use in days. Distribution and inoculations in the United States are expected to begin almost immediately thereafter.

Unidentified officials told The New York Times that the regulator is likely to grant approval on Saturday, though they cautioned that last-minute legal or bureaucratic requirements could push the announcement to Sunday or later.

If the American drug regulator grants emergency approval, the US would be the third country in the world to have authorised the use of the Pfizer/BioNTech vaccine outside of trials after the UK and Canada.

The vaccine uses messenger mRNA technology to introduce the body to the spike protein found on the outside of the coronavirus to provoke an immune response, according to The Guardian. It requires two doses, administered three weeks apart.

On Thursday, Pfizer said it planned to file for full American approval of its experimental coronavirus vaccine by April next year. The drugmaker has said it will have about 25 million doses of the vaccine for the US by the end of December. But initial supplies will be limited and reserved primarily for healthcare workers and nursing home residents, with other vulnerable groups next in line.

How the panel voted

The advisory panel, comprised of independent scientific experts, infectious disease doctors and statisticians, voted 17 to 4 that the known benefits of the vaccine outweighed the risks of taking the shot for individuals aged 16 and older, with one member of the panel abstaining.

Pfizer had asked that the two-dose vaccine be approved for use in people aged 16 to 85. It was not clear why four panelists voted against authorisation, but several mentioned they were not comfortable with including 16-and-17-year-olds, arguing the risk to those individuals was low, and the evidence in the trial was scant.

The endorsement also came despite questions about allergic reactions in two people who received the vaccine earlier this week when Britain became the first country to begin dispensing the Pfizer-BioNTech shot. An unidentified FDA official told Reuters that the agency has asked Pfizer to add severe allergic reactions to their plans to study safety issues related to the vaccine once it’s authorised.

“Despite all the remaining unknowns, in an emergency, the question is whether you know enough,” said panel member Dr Paul Offit of Children’s Hospital of Philadelphia, who concluded that the shot’s potential benefits outweigh its risks, according to AP.

Kathrin Jansen, Pfizer’s senior vice president of vaccine research and development, in her testimony highlighted the pandemic is “essentially out of control” in the US. “Modeling from the CDC [Centres of Disease Control and Prevention] shows that a vaccine with high efficacy can save many lives,” she told the advisory panel. “However, the pandemic vaccine must be introduced before the peak of cases will impact.”

The United States is the worst affected country in the world, with deaths hitting an all-time, one-day high of more than 3,100 on Wednesday.

‘Bright light in needlessly dark time’: Joe Biden

Following the vote, United States President-Elect Joe Biden called the approval “a bright light in a needlessly dark time”.

“We are grateful to the scientists and researchers who developed this vaccine,” he said in a statement. “And, we are grateful to the scientists and public health experts who evaluated the safety and efficacy of this vaccine free from political influence. The integrity of science led us to this point.”

However, the president-elect also noted that “vaccines don’t equal vaccinations”.

“Our challenge now is to scale up manufacturing and distribution to distribute 100 million shots in the first 100 days of my administration,” he said. “Before I take office, we need the Trump Administration to purchase the doses it has negotiated with Pfizer and Moderna and to work swiftly to scale manufacturing for the US population and the world. And, we will need Congress to fund our distribution efforts.”