Pfizer's vaccine strongly protects against COVID-19, U.S. regulator confirms

Documents released by U.S. regulators Tuesday confirmed that Pfizer and BioNTech's COVID-19 vaccine strongly protects against COVID-19 offering the world's first detailed look at the evidence behind the shots.

The positive review from the Food and Drug Administration sets the stage for a decision allowing the vaccine's initial use within days. FDA regulators posted their analysis online even as across the Atlantic, Britain began vaccinating its oldest citizens with the shots, which were co-developed with BioNTech.

But the U.S. judges experimental vaccines in a unique way: On Thursday, the FDA will convene what's essentially a science court that will debate in public and live streamed just how strong the data backing the shots really is. That public vetting is considered key to bolstering confidence in the shots ahead of what's expected to be the largest vaccination effort in U.S. history.

A panel of independent scientists will pick apart the FDA's first-pass review before recommending whether the vaccine appears safe and effective enough for millions of Americans. The FDA, which typically follows the committee's advice, is expected to issue a decision in the days following the review. If given the green light, the first recipients would be health-care workers and nursing home residentsaccording to plans laid out by each state.

Pfizer and its German partner BioNTech previously reported the shots appear 95 per cent effective at preventing mild to severe COVID-19 disease in a large, ongoing study. That's based on the first 170 infections detected. Only eight of the infections were among volunteers given the real vaccine while the rest had received a dummy shot.

Some protection after 1st shot

FDA's reviewers agreed that the shots were strongly protective. And of special concern, they worked about as well in older adults, too, the agency confirmed. Among volunteers over age 55, there were three cases of COVID-19 infection who were vaccinated and 48 among placebo recipients. Five of the cases were among people 75 or older, and all had received the dummy shots.

The agency's staff noted that more data would be needed to assess the potential of a single-dose shot. It said that the efficacy after the first dose and before the second dose was around 52 per cent.

WATCH |Britain begins public vaccinations Tuesday with Pfizer doses:

British woman, 90, first to receive Pfizer-BioNTech COVID-19 vaccine

4 years ago

Duration 0:48

Margaret Keenan has kicked off a global vaccination effort by receiving the first shot of the Pfizer-BioNTech COVID-19 vaccine in Coventry, England. 'Hopefully it will help other people to come along and do as I did,' she said.

A two-dose vaccination was highly effective in preventing confirmed cases of COVID-19 at least seven days after the last dose, FDA staff said.

"We're looking at the best possible data," Dr. Paul Offit of Children's Hospital of Philadelphia and an FDA adviser recently cautioned. "People worry, reasonably, how about six months later?"

The FDA staff also said that available data, while limited, suggested the people who had been previously infected with the novelcoronavirus could benefit from vaccination. Very few cases of confirmed COVID-19 occurred among participants with evidence of infection prior to vaccination, though more of those that did were in the placebo group than the vaccine group, the staff said.

FDA staff also said that the trial, which was designed to look at effectiveness against COVID-19, did not produce data to answer the question of if it also stopped infection.

READ: FDA briefing document: Pfizer-BioNTech vaccine data

The other critical issue: safety. Pfizer has reported no serious side effects. Some recipients experience flu-like reactions including fever, fatigue or muscle aches especially after the required second dose. It's a sign the immune system is revving up, able to recognize and fight back if the real virus comes along.

There were a total of six deaths in the 44,000-person trial:two deaths among those who got the vaccine and the rest in those who received a placebo, the documents showed. All deaths represent events that occur in the general population at a similar rate, FDA staff said.

Questions remain

The FDA said there was currently insufficient data to make conclusions about the safety of the vaccine in those less than 16 years of age, pregnant women and those whose immune systems were compromised.

Other questions on the FDA advisers' list:

• How well do the shots protect people at high risk such as those over age 65 or those of any age with additional health problems such as obesity or heart disease?
• Were the shots adequately tested in Black, Hispanic and other communities hard-hit by the pandemic, to know how well the vaccine works in those populations?
• Does the vaccine protect against asymptomatic infection, or could the vaccinated still unknowingly spread the virus?
• What should pregnant women be told about vaccination, since they weren't tested in Pfizer's study?

Studies in children as young as 12 are just beginning.

Emergency vaccinations could begin before Pfizer's study is complete, and answering some of those questions will require keeping that study going. Health authorities are wrestling with how to do so in a way that's fair to placebo recipients who justifiably would want to get the real vaccine.

That access "is top of mind for many," Pfizer and BioNTech recently wrote trial participants. The companies said it is exploring ways to let placebo recipients switch to the vaccine group once they meet eligibility criteria for early access if they're health workers, for instance, or when the line opens for other essential workers or people over age 65.

On the safety front, study volunteers will be monitored for two years but even studies of tens of thousands of people can't spot a complication that only strikes one in a million. So the U.S. government also is gearing up for unprecedented monitoring of recipients once emergency vaccinations get underway.

Pfizer CEO Albert Bourla declined to predict how quickly the FDA might issue a decision.

"They need to take as much time as they need to feel comfortable. It's very important for the trust of the vaccine from the people," he said at a news conference in Geneva.

It's one of several vaccines in the pipeline being tested in the hope of ending the pandemic. The FDA later this month will consider a COVID-19 vaccine by Moderna and the National Institutes of Health.

Canada has struck deals with several vaccine manufacturers, including Pfizer.

Prime Minister Justin Trudeau said it was expected that 249,000 doses would be available for distribution this month, pending regulatory approval. Government officials in Ottawa have said they don't anticipate that the Pfizer vaccine approval would significantly lag behind any U.S. approval.