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Pfizer and BioNTech surprised many industry watchers on July 27 when they announced they would conduct a large-scale study of a vaccine for Covid-19. The surprise? The vaccine that would be tested in a 30,000-patient trial wasn’t the one for which the companies had presented data on July 1.

The reason, the companies said, was that a second vaccine seemed to generate a similar immune response, but fewer side effects. On Thursday, they posted the results from all 332 people who received either vaccine, referred to as vaccines B1 or B2 — and indeed, B2 recipients experienced markedly fewer adverse events tied to the vaccine.

“Obviously, the better tolerated the vaccine, the more I think it will encourage public acceptance of a broad immunization,” said William Gruber, the senior vice president of vaccine clinical research and development at Pfizer. “Both would have been great candidates. We were fortunate that B2 actually satisfied having both a favorable immune profile and fewer reactions.”


The study tested doses of each vaccine ranging from 10 micrograms to 100 micrograms. The 30-microgram dose of B2 is being taken forward in clinical trials.

With the original vaccine, called BNT162b1, or B1 for short, patients between the ages of 18 and 55 had adverse events thought to be related to the vaccine 50% of the time at the 30-microgram dose. Those between the ages of 65 and 85 had related adverse events 16.7% of the time.


For the second vaccine, BNT162b2, or B2, patients between 18 and 55 had adverse events thought to be related to the vaccine 16.7% of the time, and no adverse effects thought to be related to the vaccine were reported in those between the ages of 65 and 85.

Both vaccines use mRNA — the genetic messenger the body uses to make the DNA code into proteins — packaged inside a fatty capsule, called a lipid nanoparticle, that allows it to get into cells. The mRNA instructs cells to make a protein, which then triggers the immune system into action. For the B1 vaccine, the mRNA coded for the part of a protein on the SARS-CoV-2 virus that binds to a receptor on human cells in order to gain entry to them. The B2 vaccine makes the entirety of this protein, known as the spike protein.

Using the full spike protein may allow the immune system to figure out more ways to detect and attack the virus. Chemical modifications to the mRNA may also explain some of the difference. Although the same dosage, by weight, was given to patients with each vaccine, the B2 vaccine would include fewer particles, because the full-length mRNA is heavier.

The side effects tracked were mostly those one would expect from a vaccine injection, including soreness at the injection site, fever, chills, headache, and muscle or joint pain. No older adult who received B2 reported redness or swelling at the injection site.

The average level of antibodies to the virus in older adults was only 41% that seen in younger participants. However, it was still higher than the level of antibodies seen in recovered patients, the authors said.

All patients in the study of B2 were white and non-Hispanic, with more older women than older men participating. The younger patients were a median of 37 years old, while the older ones were a median of 69.

Pfizer has said that some data from its large study of the B2 vaccine could come as early as October and if the vaccine is successful, the companies could seek approval as early as that month.

  • My partner and I received the B2 vaccine two weeks ago. She is Asian, and had soreness at the injection site, along with a mild fever and a raging headache for 48 hours. I had no symptoms. We are both over 70. I might have received the placebo. We will know when the results are reported.

  • page 2 of Pfizer study.

    Available Results
    Study Design and Demographics
    Between 04 May 2020 and 19 June 2020, 76 subjects were screened, and 45 participants were
    randomized and vaccinated. Twelve participants per dose level (10 μg and 30 μg), were
    vaccinated with BNT162b1 on Days 1 and 21 and 12 participants received a 100 μg dose on Day
    1. Nine participants received placebo (Figure 1). The study population consisted of healthy male
    and nonpregnant female participants with a mean age of 35.4 years (range 19 to 54 years); 51.1%
    were male and 48.9% were female. Most participants were white (82.2%) and nonHispanic/non-Latino (93.3%) (Extended Data Table 1).

    • This seem to be the same technology as the Moderna vaccine. Moderna enrolled 120 subjects in phase 1 will Pfizer enrolled only 45. I am skeptical on Pfizer’s approach. More subjects, as with Moderns vaccine, may be a better reflection of the population.

  • Why were all the patients white, non-Hispanic? I know this will be a question many ask as it’s studied further.

    • My guess is that the vaccine could react differently varying races (like ages and disabilities) but I might be wrong.

    • Austin, that seems like you’re saying that certain races are handicapped. You should really think about how racist what you said is.

  • As a former nurse-epidemiologist, I hope we do get a vaccine soon. It should be mandated except for health reasons. I believe that failure to vaccinia part of the reason the pandemic took hold. It had been statistical proven that most people receiving influenza vaccine do better if they still set flu if they have the vaccine than the unvaccinated people. I’m tired of unvaccinated people forgetting what diseases that vaccines prevent cost us as a nation!

    • Duplicating my post here because this is where it was supposed to be…As a reply to someone who wishes to force a relatively untested (long term effects) vaccination onto the public.

      And I am tired of people trying to erode my right to accept or reject something that has been rushed through studies using relatively new technology. If YOU wish to be vaccinated along with your family, that’s fine. Try to force me as an individual and I will see you in court. I am NOT an anti vaxxer, but I will wait to see how this vaccine plays out. The pharmaceutical companies are essentially immune to legal action should their vaccine have long term side effects NOT detected DURING THE RUSH TO DEVELOP AND PRODUCE.

  • I was part of the Phase 1 trial for BNT162B1 (the one not chosen) at NYU Langone. The staff there is professional and amazing. They made me feel comfortable and they deserve credit too.

    The vaccine itself caused side effects for 48 hours, but I felt fine afterward.

    • Thank you for volunteering in the early testing phase! Those of us caring for older family members are grateful to all those making potential sacrifices to get the world back to some semblance of normal!

    • My wife and I both received the b2 vaccine in Tomball Texas last week. The Pfizer staff was very professional and polite our on only side effects were arm pain and headache. We can’t wait to get the last shot… no more mask…

    • Hello Evan Fein,

      You have a lot of courage. Thank you for helping everyone on the planet. Let’s hope for the best.


  • Thank you for everyone at Pfizer for working so hard to bring help for every person possible by October for emergency use of Covid-19 vaccine. God Bless you all.

  • Good.cock.and Bill story told to an unscientific and gullible mass , belonging to certain political.interests

    • I think that’s an aggressive AI having trouble trolling people. The intent of many of these AIs are to stir partisanship.

    • A Ph.D that can’t even type a sentence correctly and throws out a generalization against an entire political party!! I wonder which political party you are aligned with??

    • I searched for Joseph Christie, PhD. Chemist at Colorado State. He died some years ago…. Another conspiracy hoax whoever this is… so many ignorant people in America these days. Smh

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