New results from a large clinical trial of Pfizer and BioNTech's experimental coronavirus vaccine showed the shot to be 95% effective in preventing COVID-19, a finding that confirms a preliminary estimate announced Nov. 9 based on an early look at the study.
Now, just over a week after lifting the world's hopes with their initial success, the partner companies report reaching the main goal of their trial, which began in late July and enrolled nearly 44,000 volunteers. One hundred and sixty-two participants who received a placebo got sick with COVID-19, compared to only eight of those who were vaccinated, Pfizer and BioNTech said Wednesday.
The 170 total confirmed cases of COVID-19 surpasses the target of 164 the companies set out as the point at which a final analysis of the vaccine's efficacy would be conducted, and is nearly double the 94 cases assessed earlier this month.
The vast majority of participants who developed COVID-19 in the trial appeared to experience mild or moderate symptoms. According to Pfizer and BioNTech, 10 severe cases were observed, nine of which occurred in individuals who received placebo. Measuring disease severity is viewed as important to determining whether vaccines can protect against the worst effects of coronavirus infection, such as respiratory failure, organ dysfunction or shock.
Crucially, Pfizer and BioNTech also now have sufficient safety data to ask the Food and Drug Administration for an emergency approval, a step the companies said they plan to take "within days." The regulator requires developers to submit a median of at least two months' worth of safety follow-up as part of any application for authorization, part of an effort to ensure no rare side effects are missed.
"We are very close to submitting for an emergency use authorization," said Pfizer CEO Albert Bourla, speaking Tuesday at an event hosted by STAT. "We will announce it as soon as we are doing it."
The FDA has pledged to hold an advisory committee meeting to publicly review any emergency approval applications for coronavirus vaccines before making a decision. A source familiar with the process told CNN the agency has scheduled a meeting for Dec. 8, 9 and 10.
The panel's deliberations would be part of an FDA review process that would likely take several weeks to complete, Peter Marks, head of the regulator's biologic drugs office, said in an Oct. 5 interview with JAMA.
Moderna, which is developing a similar type of coronavirus vaccine, also plans to soon ask the FDA for authorization. On Monday, the Cambridge, Massachusetts-based biotech reported early results from a large clinical trial showing its vaccine to be 94.5% effective in preventing COVID-19 — an outcome that makes it much more likely multiple shots could soon be available.
Moderna's finding was also based on an interim analysis conducted after 95 observed cases. Researchers overseeing the study, which enrolled 30,000 volunteers, will perform a final efficacy analysis once a total of 151 COVID-19 cases have been reported.
Pfizer and BioNTech's disclosure Wednesday is much more detailed than their initial announcement of success on Nov. 9, which stated only that an analysis of 94 COVID-19 cases in the trial found their vaccine to be "more than 90% effective."
The fuller data offer a more precise estimate, and indicate that high level of effectiveness holds up across different groups. Observed efficacy in adults older than 65 — a slice of the population at much higher risk of poor health outcomes from COVID-19 — was greater than 94%, Pfizer and BioNTech said.
Results were consistent across race and ethnicity as well, according to the companies. In the entire study, 26% of participants were Hispanic or Latino, 10% were Black and just under 5% were Asian.
No serious safety concerns related to Pfizer and BioNTech's vaccine have been found to date by a monitoring committee overseeing the trial, the companies said Wednesday. Data from some 6,000 trial participants reviewed at the interim analysis earlier this month showed most reported side effects resolved soon after vaccination.
The only more severe adverse reaction occurring in more than 2% of participants was fatigue, which was observed in 3.8% of volunteers after the second of two doses.
While the added details help to answer several key questions, more extensive data will still be needed to fully assess the vaccine's safety and to characterize how well it performs in different groups. It's still unclear, as well, whether inoculation can prevent infection as well as disease, and how long the shot's protective effects might last.
Pfizer and BioNTech said they would submit their data for peer-review and publication in a scientific journal once their analyses are completed.
Should the FDA grant an emergency use authorization in the coming weeks, the immediate challenge would turn to manufacturing and distribution, both of which are expected to be difficult to manage at scale. Pfizer and BioNTech's vaccine must be kept at ultra-cold temperatures for shipping and longer-term storage, while supplies will be very limited over the coming months.
The companies expect to manufacture some 50 million vaccines doses for use globally this year, with about half earmarked for the U.S. As the vaccine is given over two doses, that supply would cover 25 million people.
Production capacity should expand beginning in 2021, with the companies projecting they could make as many as 1.3 billion doses.
U.S. health officials recently said they expect immunizations to begin starting in December.
Editor's note: A previous version of this story referred to an outdated figure for the percent of study participants who experienced fatigue severe enough to be classified as Grade 3.