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Pfizer and BioNTech say their COVID-19 vaccine is successful in late-stage trial

A preliminary analysis of the 43,500 person study found the firms’ jointly developed mRNA vaccine 90% effective compared to placebo

by Ryan Cross
November 9, 2020


A photo of a volunteer receiving Pfizer's experimental COVID-19 vaccine.
Credit: Mark Tesk/University of Maryland School of Medicine
A graduate student at University of Maryland Baltimore was among the first to receive Pfizer's experimental vaccine.

Less than 8 months after establishing a collaboration to develop a vaccine for COVID-19, Pfizer and BioNTech say their vaccine might be safe and effective. An ongoing Phase 3 study of more than 43,000 people showed that the vaccine was more than 90% effective at preventing COVID-19—significantly besting the US Food and Drug Administration’s requirement that any vaccine be at least 50% effective for approval. It’s the first announcement of a successful late-stage trial from hundreds of groups racing to develop a vaccine.

“This is great news,” says Norbert Pardi, a messenger RNA (mRNA) vaccine expert at University of Pennsylvania, who wasn’t involved in the study. “We need to see more data, but we definitely have reason to be optimistic.”

The good news comes amidst record-breaking numbers of daily cases of COVID-19 in the US, which has already seen more than 230,000 deaths from the infection. But the results carry several important caveats. Because the announcement was made in a press release, scientists have yet to independently assess the data. The companies plan on submitting that data to a peer-reviewed publication, and the FDA has said it will be transparent about the data it uses when evaluating vaccines for approval.

Also, the trial is designed to measure cases of mild COVID-19. We don’t yet know if the vaccine is effective at preventing severe cases of COVID-19 that lead to hospitalization and death, or if it can prevent infections that lead to asymptomatic disease. We also don’t know how long it will protect people who receive the vaccine.

And there will not be enough vaccine for everyone. Pfizer says it may have up to 50 million doses—enough to vaccinate 25 million people—by the end of 2020, and up to 1.3 billion doses in 2021.

Even the vaccines on hand will not be immediately available. FDA requires that firms amass at least 2 months of safety data following vaccination before the vaccines will be evaluated for Emergency Use Authorization (EUA). Pfizer expects to have this data around the third week of November and will file for an EUA soon after. A traditional, formal approval of the vaccine—known as a biologics license application of the approval—would require at least 6 months of safety data, so most COVID-19 vaccine developers are likely to seek an EUA first.

Pfizer and BioNTech’s vaccine, called BNT162b2, is based on a still-experimental mRNA vaccine technology. The mRNA in the vaccine encodes genetic instructions for the SARS-CoV-2 spike protein, which the virus uses to enter our cells. Once injected, our cells make these proteins, giving our immune systems target practice on this crucial part of the virus without causing the disease.

Until this year, no one had tested an mRNA vaccine in a large, Phase 3 clinical trial. BNT162b2 and another advanced mRNA vaccine for COVID-19 made by Moderna could become the first FDA-authorized mRNA vaccines this year or early next.

In the Pfizer trial, half of the participants received two doses, administered 3 weeks apart, of BNT162b2, while other half got two placebo shots. The preliminary data were reviewed by an independent committee after 94 people in the trial developed COVID-19. The committee determined that the vaccine was more than 90% effective compared to the placebo—suggesting that most of the COVID-19 cases were from people who got placebo shots. The efficacy was based on data collected just 1 week after participants got their second shot.

Pardi is excited that the vaccine appeared to work so quickly, as it can sometimes take a few weeks for the protective levels of antibodies induced by a vaccine to kick in. “I don’t want to oversell this,” he says. “But I think the protective efficacy of the vaccine will be even higher a couple of weeks later.” The companies have yet to provide data on antibody or T cell levels generated in the participants who received the vaccine, and Pardi says that it will be important to study that immune response for several months to understand if immunity lasts.

Although Pfizer said that over 30% of US participants in the trial were from racially and ethnically diverse backgrounds, it has not indicated whether there were any differences in the vaccine’s efficacy among these groups. It also didn’t mention data sorted by age, which is a major factor in how well a vaccine works.

The vaccine, if approved, will face logistical and distribution challenges, as it requires storage at –80 °C. The US government placed a $1.95 billion preorder for 100 million doses of the vaccine back in July, with the rights to purchase up to 500 million more doses. Unlike other COVID-19 vaccine front-runners—AstraZeneca, Johnson & Johnson, Moderna, Novavax, and Sanofi Pasteur—Pfizer and BioNTech did not receive funding from the US government to develop and test their vaccine.

The US government has said it will distribute vaccines that it purchases from these developers for free, but Michael Kinch, director of the Center for Research Innovation in Biotechnology at Washington University in St. Louis, points out that the companies could make more money in the future if we end up needing booster shots annually or every few years. “They may not make their money upfront, but they could have a lucrative income stream until their patents run out. And we may need these vaccines for the rest of our lives.”

As the first to announce the effectiveness of its vaccine in a Phase 3 study, Pfizer set a high bar for other companies to follow, says Michael Haydock, an analyst at Informa Pharma Intelligence. “That said, you have to be a little careful comparing different trials,” he adds. For instance, since vaccines are typically less effective in elderly people, the proportion of these individuals in the trial will likely shape the results.

On Nov. 11, 2 days after Pfizer’s announcement, the Gamaleya National Center of Epidemiology and Microbiology in Moscow said that its COVID-19 vaccine was 92% effective in a preliminary analysis of its Phase 3 trial. The vaccine consists of two shots, each containing a different adenoviral vector that delivers genetic instructions for the coronavirus spike protein into human cells.

At the time of the announcement, more than 16,000 people in the planned 40,000 person trial had received two injections of the vaccine or a placebo, and 20 people had developed COVID-19.

Russia issued an emergency use authorization for the vaccine 3 months ago, even though at that time it had only been tested in dozens of people. Gamaleya says the vaccine since has been administered to more than 10,000 medical workers and other unspecified high-risk groups.


This story was updated with additional reporting on Nov. 11, 2020.




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