Severe Allergic Reaction to a COVID-19 Vaccine


If you get a COVID-19 vaccine and you think you might be having a severe allergic reaction after leaving the vaccination provider site, seek immediate medical care by calling 911.

If you had a severe allergic reaction—also known as anaphylaxis—after getting a shot of an mRNA COVID-19 vaccine (either Pfizer-BioNTech or Moderna), CDC recommends that you not get another shot of that vaccine. Learn which COVID-19 vaccines need a second shot.

A severe allergic reaction can cause a rapid heartbeat, difficulty breathing, swelling of the throat, or a generalized rash or hives. A person with a severe allergic reaction needs to be treated with epinephrine or EpiPen© or they must go to the hospital. Learn about common side effects of COVID-19 vaccines and when to call a doctor.

Possible Side Effects After Getting a COVID-19 Vaccine

COVID-19 vaccination will help protect you from getting COVID-19. You may have some side effects, which are normal signs that your body is building protection. These side effects may affect your ability to do daily activities, but they should go away in a few days. Some people have no side effects.

Serious side effects that could cause a long-term health problem are extremely unlikely following any vaccination, including COVID-19 vaccination. Vaccine monitoring has historically shown that side effects generally happen within six weeks of receiving a vaccine dose. For this reason, the FDA required each of the authorized COVID-19 vaccines to be studied for at least two months (eight weeks) after the final dose.

Common Side Effects

On the arm  where you got the shot:
Throughout the rest of your body:
  • Tiredness
  • Headache
  • Muscle pain
  • Chills
  • Fever
  • Nausea
Here are some examples from Twitter below. 

A study published in the peer-reviewed journal Acta Médica Portuguesa has found the rate of anaphylactic shock in response to the COVID vaccines is 400% higher compared to the normal rate for vaccines. And in the case of the UK's Oxford/Astra-Zeneca COVID vaccine, the rate is at least 1,000% higher than the normal level.

According to the study, the FDA's data released since January 18, 2021 shows an allergic reaction rate of 4.7 anaphylactic shock reactions per million vaccinations for the Pfizer vaccine and 2.5 anaphylactic shock reactions per million for the Moderna vaccine. This is significantly higher than the average safety threshold of less than one reaction per million vaccinations. 

This is important because, according to the study on page 544, this reaction could be life-threatening because some who experience anaphylactic shock could stop breathing if their airways close and the proper medical procedures are not administered in time to open up the airways. 

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