Pfizer's coronavirus vaccine is more than 90% effective, early data suggests

A vaccine.
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Early data suggests that Pfizer's coronavirus vaccine is more than 90% effective in preventing an infection with the virus that causes COVID-19, the company announced on Monday (Nov. 9). 

The vaccine, developed by Pfizer and German drug company BioNTech, is currently being tested in a large phase 3 clinical trial — the last and most critical stage of testing in which vaccines must prove to be safe and effective in a large group of people — that began in late July. 

An external independent Data Monitoring Committee conducted an interim analysis of the trial by evaluating 94 participants who developed COVID-19 after receiving either the vaccine or the placebo — a control measure that has no impact on preventing the infection.

Related: The most promising coronavirus vaccine candidates

The early analysis revealed that among these 94 participants, fewer than 10% of those who received two injections of the vaccine, 28 days apart, developed COVID-19. In other words, most of the cases, more than 90% of them, were among those who received the placebo.

However, this 90% efficacy was announced in a press release, and the companies haven't yet released actual data on the trials. The data has not been peer-reviewed or published in a medical journal. As the phase 3 trial continues, this percentage may vary, the company said in the statement. 

Though the results aren't yet conclusive, if the numbers hold up, they are much higher than expectations.

"This is really a spectacular number," Akiko Iwasaki, an immunologist at Yale University told The New York Times. "I wasn’t expecting it to be this high. I was preparing myself for something like 55 percent." Indeed, the Food and Drug Administration (FDA) has said that in order for a vaccine to be approved, it would have to be at least 50% effective.

If the number holds up, "that is huge," Dr. Ashish Jha, the dean of the School of Public Health at Brown University, told STAT News. "That is much better than I was expecting, and it will make a huge difference." However, he cautioned that researchers will need to see full results before making any conclusions.

The phase 3 clinical trial has enrolled 43,538 participants to date across the U.S., Argentina, Turkey, Brazil, Germany and South Africa. Around 30% of U.S. participants and 42% of global participants have racially and ethnically diverse backgrounds, according to the statement. 

Originally, the interim analysis was set to be conducted when 32 people had developed COVID-19, but after discussions with the FDA, that number was bumped up to at least 62 people, according to the statement. The trial will continue to enroll participants until the final analysis when 164 participants test positive for  COVID-19, according to the statement. 

The study will further evaluate whether the vaccine provides protection for those who have previously been infected with SARS-CoV-2 and if the vaccine reduces severity in vaccinated people who do develop COVID-19, according to the statement. 

"Today is a great day for science and humanity," Dr. Albert Bourla, CEO and chairman of Pfizer, said in the statement. "We are reaching this critical milestone in our vaccine development program at a time when the world needs it most with infection rates setting new records, hospitals nearing over-capacity and economies struggling to reopen."

The companies will apply for an emergency use authorization (EUA) once they have gathered two months of safety data after participants received the second dose of vaccine — a milestone that could be reached in the third week of November, according to the statement. The companies expect to produce up to 50 million vaccine doses globally in 2020 and up to 1.3 billion doses in 2021, according to the statement. 

Pfizer's candidate coronavirus vaccine uses the same technology as Moderna's, another vaccine that's in late-stage testing: It uses a genetic messenger called mRNA to prompt the immune system to recognize the virus, Live Science reported. No vaccine that uses this technology has yet been approved for any virus. Even so, this type of vaccine may have several advantages over traditional vaccines, such as being quicker and easier to manufacture. However, the Pfizer vaccine requires ultra-cold storage at minus 94 degrees Fahrenheit (minus 70 degrees Celsius), which could make distributing and administering the vaccine more challenging. (Moderna's vaccine requires storage at ordinary freezer temperatures.) 

Pfizer and BioNTech's vaccine is just one of a handful of candidate coronavirus vaccines that are currently in late-stage clinical trials. These interim results, the first to be announced from any late-stage clinical trial for coronavirus vaccines, come as the U.S., Europe and other parts of the world are  inundated with another massive wave of coronavirus infections. 

Originally published on Live Science.

Yasemin Saplakoglu
Staff Writer

Yasemin is a staff writer at Live Science, covering health, neuroscience and biology. Her work has appeared in Scientific American, Science and the San Jose Mercury News. She has a bachelor's degree in biomedical engineering from the University of Connecticut and a graduate certificate in science communication from the University of California, Santa Cruz.

  • Sharona Pius
    I think it's a bit early to call an effective vaccine. I do hope it's effective enough to save lives, but the Coronavirus has already undergone some significant mutations.
    In Denmark, veterinary workers culled 17 million mink to try and halt a mutated strain that jumped from animals to humans. It was traced back to mink farms.
    "The animals were carrying a new strain of the virus, possibly vaccine-resistant, and infected several hundred people "
    The vaccine may be 90% effective for the particular strain of COVID-19, the question is, how will they affect a mutated form of this virus.
    I don't know. It just doesn't add up. Highly unlikely that it will make any real impact.... sorry.
  • Chem721
    Sharona Pius said:
    Highly unlikely that it will make any real impact.... sorry.

    It is too early to make a call on any mutations impacting the effectiveness of the vaccines under development. It must be known where the mutation(s) have occurred, and what if any impact they have on antibody binding affinity. Of course it also depends on the extent such virus mutants can spread. If they are eliminated by local mitigation, there is no serious threat. That is why they are killing off so many mink. These variants aren't even close to a mass European presence, much less a global one.

    Any spread would also depend on how infectious any mutant form is. Any mutants arising on mink farms will have to compete with other strains which already occur in much greater numbers. That they might replace existing strains and threaten a vaccine is far from certain.

    In short, the less infective a mutant form, the less likely it will be highly represented in the global pool of strains infecting people. This story from the mink farms is far from definitive. More data is required before any hard conclusions can be drawn. But it is one reason to eliminate the virus asap, as the more it mutates, the less effective any or all vaccines will become. Which is why any vaccine may only be good for a year or two.
  • dr abduljabbar
    there are more than 16NSPs:1-16 and (nonstructural proteins) and Envelope Protein as well : virus liberatorORF19: and mystery protein s (10) and NUCLEOCAPSID PROTEIN N and many more such as the PROTEASE so the question is which from all of these structures is stable and included in the vaccine to promote protection by vaccination.which is the most valid piece is inthe vaccine thanks
  • Chem721
    dr abduljabbar said:
    the question is which from all of these structures is stable and included in the vaccine

    The Chinese are reportedly using an inactivated form of the virus and apparently have used it on hundreds of thousands of people. This would certainly have the potential to "offer" all external viral antigens to the immune system to form antibodies. If they are neutralizing antibodies without significant ADE, this would likely be ideal.

    However, most vaccines have concentrated on the spike protein only, since it has the receptor binding domain. Interfering with this protein has the highest potential for success, or so it would seem. But other viral surface antigens could also elicit neutralizing immunity with less risk for evasion by viral mutations since multiple mutations on various proteins would have to appear on the same virion for it to evade antibody-binding and likely elimination.

    It must be remembered that all who have survived viral infection were exposed to all those external proteins, and not just the spike. Clearly the intact virus offers some form of "lasting" immunity. The biggest questions which remain are effectiveness, adverse reactions for any vaccines under development, and longevity of immunity.