Update (November 18, 2020):
Just a week after initial data suggested Pfizer’s COVID-19 vaccine was more than 90% effective, a final report on a large phase 3 clinical trial of the vaccine suggests it may be even more impressive than that.
The full trial involved over 41,000 participants, half of whom received two doses of the vaccine while the other half received a placebo. Among those participants, there were 170 confirmed cases of symptomatic COVID-19—and 162 of those occurred in the placebo group, according to a press release. That led the researchers to conclude that the vaccine is 95% effective at preventing symptomatic COVID-19 infections.
However, this is still just a preliminary result from a press release. The company hasn’t published a full study and the vaccine hasn’t been approved by the Food and Drug Administration yet. So we don’t know conclusively how effective the vaccine is at protecting against coronavirus infections, with or without symptoms. But it’s certainly an encouraging sign! To learn more about the vaccine and the data behind it, continue to our original report below.
Original report (November 9, 2020):
Pfizer just released some early information about its COVID-19 vaccine, which appears to be successful at preventing symptoms of the infection. So far, Pfizer’s COVID-19 vaccine data has experts cautiously optimistic.
The announcement comes after an early analysis of data from a Phase 3 trial of the vaccine, which enrolled more than 43,000 participants and is still recruiting, according to a press release. Half of those participants received a placebo, and the other half got the vaccine candidate, which Pfizer is developing along with BioNTech.
Among all the participants, there have been 94 symptomatic cases of COVID-19. Based on how many participants got the vaccine and the infection versus those who received the placebo and developed the infection, the company concluded that its vaccine is over 90% effective at preventing symptomatic COVID-19 infections. It’s not clear exactly how many people in each group got the coronavirus or how effective the vaccine is at preventing asymptomatic infections.
Considering that the Food and Drug Administration (FDA) said it would consider approving a vaccine that was just 50% effective at preventing the infection or reducing the severity of its symptoms, these results are a pleasant surprise for public health experts. The results are “just extraordinary,” Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases, told the AP. “Not very many people expected it would be as high as that.”
Other experts also say these results are encouraging but caution that we don’t know the full picture of how effective the vaccine really is. “That’s a big reduction in symptoms, but it’s not clear that this vaccine is effective at preventing infection altogether,” Angela Rasmussen, Ph.D., a virologist at Columbia University School of Public Health, said on Twitter. We also don’t know how well the vaccine works in people with underlying conditions—diabetes, asthma, heart disease, etc.—that might make them more vulnerable to severe COVID-19 complications, she said. And because the vaccine has only been studied for a few months, we don’t know how long its protection lasts, Ali Nouri, Ph.D., molecular biologist and president of the American Federation of Scientists, said on Twitter.
It’s also important to remember that the trial is ongoing and these results aren’t complete. “While the results are exciting, of course we will want to independently evaluate them,” Natalie E. Dean, Ph.D., assistant professor of biostatistics at the University of Florida, explained on Twitter. “Unlike treatments, promising data from vaccines do not immediately change standard of care. The vaccines will undergo a rigorous review process first which will play out over time.”