Pfizer and BioNTech on Monday announced that early data from a trial of their coronavirus vaccine candidate shows the vaccine is more than 90% effective in preventing Covid-19—but experts caution that while the results exceed expectations, it's important to be cautious and wait for the full findings.
Pfizer's coronavirus vaccine more than 90% effective
The companies currently are conducting a Phase 3 clinical trial of their mRNA-based vaccine candidate, BNT162b2. The vaccine—which is delivered via two doses, administered three weeks apart—uses genetic material known as messenger RNA (mRNA) that is injected into muscle cells. The vaccine then produces proteins in the body that can trigger an immune response to combat the virus.
The companies originally planned to evaluate the candidate's efficacy once 32 of the 43,538 people enrolled in the trial contracted Covid-19—that is, tested positive for the virus and presented with at least one symptom—and would continue until at least 164 cases of Covid-19 were reported.
However, after consulting with FDA, the companies opted to do their first review after 62 cases of Covid-19 had been identified. But by the time they came to that decision, there were 94 cases of Covid-19 in the study. Based on the data at that point in time, a panel of independent experts found that the vaccine was 94% effective in preventing Covid-19 among people who have not previously been infected with the new coronavirus. Specifically, among individuals who were vaccinated, there were 94% fewer cases of symptomatic Covid-19 than among those who received a placebo at seven days after second dose.
The independent panel shared its findings with Pfizer and BioNTech, which issued a press release announcing the results. The data has not yet been peer-reviewed or published in a medical journal.
Pfizer and BioNTech have not publicly released data yet on whether the vaccine is effective at preventing severe cases of Covid-19, nor is there evidence on whether the candidate prevents people from contracting SARS-CoV-2, the virus that causes Covid-19. The companies also do not yet know how long the vaccine provides protection against the new coronavirus.
The vaccine has been shown to have side effects, including aches and fevers. According to William Gruber, Pfizer's SVP of vaccine clinical research and development, the side effects of the vaccine—including aches and fever—are comparable to other adult vaccines but are likely worse than the pneumonia vaccine developed by Pfizer or a flu shot.
According to STAT News, Pfizer's Phase 3 trial of the candidate is ongoing, and additional findings could affect the reported results.
That said, Pfizer indicated it may soon request FDA emergency use authorization (EUA) for the vaccine. According to Pfizer, in accordance with FDA guidance, the company will not file for an EUA until at least half of vaccinated trial participants have been monitored for safety issues stemming from the vaccine for a minimum of two months following the second dose. Pfizer said it expects to meet that milestone by the third week of November, at which point they expect to request an EUA.
Overall, Pfizer said it intends to have enough doses of the vaccine manufactured by the end of the year to immunize 15 to 20 million people, with 1.3 billion available globally in 2021. However, there may be distribution challenges, as the vaccine candidate must be stored at very cold temperatures, making it difficult to deliver the vaccine to certain locations.
'This is extraordinary'
Many experts were encouraged by Pfizer's early results, but they emphasized caution until more results are released.
"I've been in vaccine development for 35 years," William Gruber, senior VP of vaccine clinical research and development at Pfizer, said. "I've seen some really good things. This is extraordinary."
"If that headline number really holds up, that is huge," Ashish Jha, dean of the School of Public Health at Brown University, said. "This really bodes well for us being able to get a handle on the epidemic and get us out of this situation." However, Jha cautioned that it's difficult to evaluate trial results through a press release and said researchers need to see the full results, noting that side effects are important to watch.
Similarly, Michael Head, senior research fellow in global health at the University of Southampton in the United Kingdom, said, "We should remain a little cautious. The provision findings are made available in a press release, and the study is ongoing" (Herper, STAT News, 11/9; Thomas et. al., New York Times, 11/9; Hopkins, Wall Street Journal, 11/9; Morello, Politico, 11/9).