Friday’s COVID Vaccine update — Comparing the Two mRNA Vaccines

Patients and friends are asking about the two extremely effective mRNA vaccines against COVID-19 (caused by the coronavirus SARS-CoV-2) from Pfizer/BioNTech and Moderna compare. Here is a nice summary of the differences in each that was prepared by my friends at

How the two mRNA Vaccines Compare

Efficacy After 1st dose: 52% (Some protection as early as 10 days after 1st dose).

After 2nd dose: 95%

After 1st dose: Not known

After 2nd dose: 94% (Efficacy in those 65 and older is a little lower, about 86%; however, overall, some evidence of greater protection against severe disease)

Most Common Side Effects Injection site pain, fatigue, headache, muscle pain, chills, joint pain, fever; more common after 2nddose Injection site pain, fatigue, headache, muscle pain, joint pain, chills, nausea/vomiting, fever; more common after 2nd dose. Higher rate of side effects than with Pfizer. Facial swelling in 2 people with a history of cosmetic filler injections has also been reported 1-2 days after last dose.
Duration of side effects Can last several days Typically one day, but can last up to one week
Serious allergic reaction No increased risk seen in clinical trials but has been reported on 1st dose during roll-out. Treatable with epinephrine. Affected people should not receive a second dose. No increased risk seen in clinical trials but has been reported on 1st dose during roll-out. Treatable with epinephrine. Affected people should not receive a second dose.
Where to Get Requires very low-temperature storage, so availability may be more limited to hospitals and specialized settings. Requires only regular refrigeration, so may be more broadly available, such as in doctor’s offices, clinics, rural locations.
Ingredients (per dose)

(Note: PEGis polyethylene glycol)

  • 30 mcg nucleoside-modified mRNA
  • Lipids (fatty substances)
    • (4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate)
    • 2[PEG 2000]-N,N-ditetradecylacetamide
    • 1,2-distearoyl-sn-glycero-3-phosphocholine
    • Cholesterol
  • Potassium chloride
  • Monobasic potassium phosphate
  • Sodium chloride
  • Dibasic sodium phosphate dihydrate
  • Sucrose (sugar)
  • 100 mcg nucleoside-modified mRNA
  • Lipids (fatty substances)
    • SM-102
    • PEG 2000 dimyristoyl glycerol (DMG)
    • Cholesterol
    • 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)
  • Tromethamine
  • Tromethamine hydrochloride
  • Acetic acid
  • Sodium acetate
  • Sucrose (sugar)

*The CDC has recommended that people who experience anaphylaxis after the first dose of the COVID-19 vaccine should not receive additional doses (CDC, 2020).
Sources: FDA Fact Sheet for Administering Moderna COVID-19 Vaccine; FDA Fact Sheet for Administering Pfizer COVID-19 Vaccine; Polack, N Engl J Med 2020; Mahase, BMJ 2020; New York Times (12/16/02)

This blog was accurate as of the day of posting. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus and the COVID vaccine develops, the information above may have changed since it was last updated. While I aim to keep all of my blogs on COVID and the COVID vaccine up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news.

© Copyright WLL, INC. 2021. This blog provides a wide variety of general health information only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment from your regular physician. If you are concerned about your health, take what you learn from this blog and meet with your personal doctor to discuss your concerns.


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5 Responses to Friday’s COVID Vaccine update — Comparing the Two mRNA Vaccines

  1. Kim Donahue says:

    I had the Pfizer vaccine and I have been having really bad headaches. Also my sed rate is very high, my c reactive protein is elevated along with my thyroid levels. Is this normal?

  2. Kim,

    Of course, this is not normal. If you have not already, contact your healthcare professional about these signs and symptoms as soon as possible. Prayerfully, your physician can find the source(s) for all this. They will want to determine if these issues were caused by the vaccine or are just coincidental with receiving it. Also, if you think it’s possible this is all even possibly related to the vaccine, a Vaccine Adverse Event Reporting System (VAERS) report should be filled out. You can learn more at Let me know what is determined.

    Dr. Walt

  3. Dan Ostergaard, MD says:

    Walt, thanks very much for your timely and excellent information about the virus and now especially about the vaccine!
    I am asked vaccine questions by members of our Zoom Sunday School Class and your personal advice and that of your resources are very valuable.
    To all, always wear a good mask and get vaccine as soon as you can!
    Blessings, Dan

  4. Thanks, Dan. Barb and I have both had two doses of the Moderna vaccine. Minimal arm soreness. Since my antibody test is positive. Thank the Lord for the vaccine.

    Love to you both.


  5. Diane O'Connor says:

    Bland and I both have had the 2 doses of the Pfizer vaccine. We were both 1b as he is 70 and I am a healthcare provider( Dental Hygienist- #1 occupation at risk of contracting Covid 19). Sore arm for a day dose 1 and redness at injection site for a day dose 2. Grateful and blessed.

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