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Pfizer and BioNTech announced Wednesday that the efficacy portion of their Covid-19 vaccine trial has been completed, showing the vaccine to prevent 95% of cases of the disease.

The companies said that they plan to submit to the Food and Drug Administration for an emergency use authorization “within days,” and will also submit to regulatory agencies around the globe.


The results come little more than a week after the companies said an earlier analysis from the study showed the vaccine reduced infections by more than 90%, and just days after another company, Moderna, said that a similar vaccine reduced infections by 94.5%. Taken together, the results raise hopes that vaccines will be broadly available sometime next year, and also, perhaps, that other vaccines against the disease will also prove effective.

In a conversation at the STAT Summit Tuesday, Pfizer CEO Albert Bourla said that viewing the earlier data on the efficacy of the vaccine had been a high point in his life. “When I heard the over 90% efficacy, I felt I was living a dream,” he said.

Of the 170 cases of Covid-19 Pfizer observed in its trial, 162 occurred in the placebo group and just eight among the group that got its two-dose vaccine. Of the 10 cases of severe Covid-19, nine were in the placebo group, an important finding which suggests the vaccine prevents not only mild cases, but the type of serious disease that leads patients to die or be hospitalized.


In the early look at the Moderna trial, which is not yet complete, there were 11 cases of severe disease, all in the placebo group.

It is not clear how long the efficacy of either vaccine will last, in part because they have been developed at such dramatic speed.

“I take one step at a time,” Anthony Fauci, the director of the National Institute for Allergy and Infectious Diseases, said Tuesday at the STAT Summit. “I’ll take the 94.5% effective for now,” he said of Moderna’s interim analysis this week, “and we’ll worry about the durability of the effect” next.

Pfizer said that no serious safety concerns related to the vaccine were reported in its study, which included 43,661 volunteers. Data on common side effects was tracked in an 8,000-patient portion of the study. The only severe side effects to occur in more than 2% of people were fatigue, which occurred in 3.7% of patients after the second dose, and headache, which occurred in 2%. Older adults had fewer and milder side effects than younger participants. Approximately 19,000 participants in the study have been followed for at least two months since their second dose of the vaccine.

Pfizer’s updated results follow Moderna’s report that its Covid-19 vaccine, using similar technology, reduced the risk of Covid-19 by 94.5% in interim results from a 30,000-volunteer clinical trial. Moderna observed 95 cases of symptomatic Covid-19, only five of which affected participants who received the company’s vaccine.

In Moderna’s study, there were 11 cases of severe Covid-19, all of which occurred in the placebo group. Moderna said there were no significant safety concerns observed in the trial. Severe events that occurred in greater than 2% of patients included fatigue, muscle pain, headache, and achiness. These events were “generally short-lived,” the company said in a press release.

Like Pfizer, Moderna plans to file in the coming weeks for emergency use authorization from the FDA once it has collected further safety data. That would allow its vaccine to be distributed to people at high risk for Covid-19.

Pfizer and Moderna both use messenger RNA, or mRNA, technology in their vaccines. Each strand of synthetic mRNA is designed to encode for a protein found on the surface of SARS-CoV-2, the virus that causes Covid-19. Those mRNA strands enter the body’s cells and instruct them to produce that protein. The immune system then recognizes it as a foreign invader and produces antibodies that protect against Covid-19 if a person is later exposed to the virus.

Supplies of both vaccines are likely to be limited for months to come. Pfizer has said it could produce up to 50 million doses by the end of the year. Moderna, whose vaccination also requires two doses, has promised as many as 20 million in the same time frame. In 2021, Pfizer expects to manufacture about 1.3 billion doses, while Moderna will make between 500 million and 1 billion.

The Pfizer-BioNTech vaccine needs to be kept at very cold temperatures, which has raised concerns about the possible rollout of the vaccine. On Tuesday, Bourla said he expected that distribution issues would be manageable. “I think people will be surprised how smoothly the whole operation will go,” he said.

Pfizer, which did not accept research funding from the federal Operation Warp Speed initiative, has agreed to supply 100 million doses to the U.S. government in exchange for $1.9 billion. The U.S. has the option to buy 400 million more. Moderna received about $1 billion in federal funds to support its vaccine development and has agreed to provide 100 million doses to the U.S. for $1.5 billion.

About 30% of U.S. volunteers in Pfizer’s trial are people of color, the company said. Roughly 45% of U.S. participants are between the ages of 56 and 85, a group at particularly high risk for severe Covid-19. About 37% of volunteers in Moderna’s 30,000-volunteer trial were people of color, according to the company.

  • They have no indication of long term side effects as they have not Been texting that long what’s to say 1 year down the riad this drug effects other organs has nit bern tested long enough to just go get vaccine and hope it does nothing else to your body
    I agree we need something but to just get a vaccine without proven facts us nit something i am willing to do

    • I don’t mind taking it, I’m 22 healthy and for my age range the mortality rate EVEN IF I contract the virus is < 0.008% even lower for teenagers who middle school to high school age, 16 times of that of my age comparison group. Source is from the CDC hospitalization and death rate.

    • We are in a Public Health Emergency and a National Emergency. About 1300 Americans are dying of COVID every day.

      Is this really the time for people over 60 to worry about a possible ( 1 in a million, maybe) long term rash as the possible price for a life-saving vaccine?

      Perhaps after another 100,000 Americans die with COVID, vaccines that millions have already taken will look more compelling.

  • Just super curious: have the mechanisms and efficacy been tested on people that were COVID positive, recovered, then received the vaccine? With testing being widely available, but not available enough, many people who may have already contracted COVID may be getting the vaccines. I’d still get the vaccine myself regardless out of caution, I’m just curious if this was something they took into account for the trials.

    • Asymptomatic, but antibody positive participants were included. If you were a laboratory confirmed, symptomatic COVID case then you were excluded from the trial.

      All participants were swabbed for current infection at the first appointment, and tested for antibodies. At the second appointment, you were swabbed again for current infection. 1 month after receiving the second dose, you were brought in again to test for vaccine-derived antibodies (which can be distinguished from natural, infection-derived antibodies). Presumably, even if you were in the placebo arm, your sample would have been analyzed for naturally derived antibodies.

  • I’m not sure I understand what reducing infections by 94.5% actually means. Does that mean 5.5% of those vaccinated get the infection? Where I live, current daily positive cases vs daily negative tests seem to indicate about an 11% positive infection rate or 89% negative infection rate without a vaccine. So, out of 1,000 people, 110 should be expected to get Covid-19 naturally whereas 55 would be expected to get it with the vaccination? Am I looking at this incorrectly?

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