My Patients Ask: Can COVID vaccines cause side effects in most people?

No. Side effects such as fatigue or headache occur in under five percent of participants. Less than two percent developed muscle aches or fever.

However, almost everyone taking the vaccine will experience transient soreness at the injection site.

Nevertheless, all of these reactions typically resolve within 48 hours and are a normal response to vaccines — one that shows it is working as intended.

UCHealth is recommending patients take acetaminophen (as opposed to ibuprofen) as needed AFTER the vaccine.

DO NOT TAKE NSAIDs (like ibuprofen or naproxen) BEFORE taking the vaccine.

SEVERE REACTIONS such as anaphylaxis are exceedingly rare occurring at a rate of about 5 per million with the Pfizer vaccine and about 3 per million with the Moderna vaccine.


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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4 Responses to My Patients Ask: Can COVID vaccines cause side effects in most people?

  1. Sus Schmitt says:

    Thanks! Very helpful.

  2. Glad to hear. Stay safe!

    Dr. Walt

  3. Linda Watkins says:

    Bruce had no effects from first or second. I had no effects from my first. (Pfizer)

  4. Hey Linda,

    Your experience will be what happens to over 90% of those who take the mRNA COVID vaccines (or, should I say what does NOT happen!). :-)

    These vaccines (Moderna and Pfizer) are extraordinarily safe and effective.

    Dr. Walt

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