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March 12, 2021 • read

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Allergic reactions from the COVID-19 vaccine

With COVID-19 vaccines being distributed across the country, we’re a step closer to the virus being a thing of the past. A few people who’ve already gotten the jab reported allergic reactions. Though allergies to vaccinations aren’t common, they’re also not unheard of. Here’s information about vaccines and allergies, and what to consider before getting a COVID-19 shot.

What are vaccines made of?

Vaccines help prime your immune system to fight a specific disease. They’re made of a dead or weakened sample of the pathogen. There are other ingredients frequently used in vaccines too. Their purpose is to help keep the vaccine stable while it’s in storage, prevent contamination, and increase its potency. Other ingredients commonly found in vaccines include:

  • Amino acids
  • Sugars
  • Proteins
  • Salt
  • Trace amounts of ingredients that were used to kill the germ in a vaccine, like formaldehyde

The United States Food and Drug Administration has a full list of ingredients in each vaccine.


Sometimes multiple doses of a vaccine are stored in one container. Preservatives help keep any unused doses of the vaccine in an open container from being contaminated by fungi or bacteria. This prevents serious infection. 


Antibodies are disease-fighting proteins. Your body creates them when exposed to a new disease, such as through vaccination. The more antibodies your body creates, the more stronger your immune response. Vaccinations help prime your immune system for a stronger response to fight the disease. 

When your immune system is producing antibodies to fight a disease, your B and T cells activate. B cells are bone marrow cells, and T cells are cells from a gland called the thymus. B cells help fight any disease in your body that lives outside of your cells. T cells, on the other hand, fight any diseases that thrive inside your cells. Adjuvants are substances that boost your body’s immune response by keeping B and T cells activated for longer periods. This helps your immune system create more antibodies, and thus a stronger immune response. 

Aluminium salts is one example of a commonly used adjuvant in vaccines allowed in Canada. The list of allowed ingredients is approved by Health Canada. 

Vaccines and allergic reactions

Although rare, it’s possible for allergic reactions to occur from any vaccine.

Some people confuse the common side-effects of vaccination with having an allergic reaction. They’re not quite the same thing. Side-effects usually kick in 12 hours after your shot, and last up to 36 hours. They may include:

  • Mild fever
  • Soreness around the injection site
  • Redness, pain, swelling, or itchy skin around the injection site
  • Muscle pain
  • Loss of appetite
  • Chills
  • Fatigue
  • Joint pains
  • Headache

In some instances, more severe reactions could include:

  • High fever, above 40°C
  • Seizure
  • Fainting


Anaphylaxis is a potentially life-threatening allergic reaction. Thankfully, it’s reversible when treated quickly with an EpiPen. The likelihood of anaphylactic shock from a vaccine is between one and 100,000 and one in one million. Although it’s extremely rare, it’s important to seek immediate medical attention if you notice any of the following symptoms after getting your shot:

  • Facial swelling
  • Falling to the floor
  • A sudden drop in blood pressure
  • Abdominal pain
  • Difficulty breathing
  • Itchy rash
  • Sneezing, coughing, or vomiting

What’s in the COVID-19 vaccine?

There are four COVID-19 vaccines currently approved in Canada. They’re from Pfizer-BioNtech, Moderna, AstraZeneca, and Janssen. The allergic reactions that have been reported in Canada so far are mostly from people who’ve received the Pfizer vaccine.

The list of ingredients in the Pfizer vaccine include:

  • Medicinal ingredient:
    • mRNA
  • Non-medicinal ingredients:
    • ALC-0315 = ((4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate)
    • ALC-0159 = 2-[(polyethylene glycol)-2000]-N,N-ditetradecylacetamide
    • 1,2-Distearoyl-sn-glycero-3-phosphocholine
    • cholesterol
    • dibasic sodium phosphate dihydrate
    • monobasic potassium phosphate
    • potassium chloride
    • sodium chloride
    • sucrose
    • water for injection 

Every vaccine goes through trials before use on the public. Details about common reactions to a vaccine are reviewed by public health officials before approval. With the Pfizer vaccine, allergic reaction symptoms also showed up during the vaccine trials. That’s good news, because it means there aren’t any unusual reactions to the Pfizer vaccine so far. That’s also why the vaccine is still considered safe to use. Experts say the risks of an allergic reaction aren’t as serious as the risks from going without vaccination. 

What to do if you’re worried you might be allergic

It’s natural to be concerned about the safety of a new medicine. If you had an allergic reaction to your first dose of the COVID-19 vaccine, consult a doctor before getting your second dose. Allergic reactions can worsen with repeat exposure to the allergen, so you might have a more serious response to the second injection. An allergist can help you understand your risk for an increased allergic response.

Think of whether you’ve had a bad reaction to vaccinations in the past. If you have a history of allergies to medicine, an allergist can help you determine if either of the two vaccines are right for you. If you haven’t ever had a reaction to medicine, there’s no evidence to suggest you’re at higher risk with the COVID-19 shots.

To make an informed decision, consider:

  • Reading the COVID-19 ingredients list.
  • Consulting an allergist. An allergist will be able to help you assess your risk for an allergic reaction based on your medical history. 
  • Your current health. If you’re immunosuppressed or pregnant, you may not be eligible to get vaccinated. When in doubt, consult a medical professional.
  • Your history of severe allergic reactions to vaccinations. If you’ve experienced anaphylaxis after getting a vaccination in the past, work with a doctor to pinpoint what caused the reaction. 
  • Your history of severe allergic reactions to food, insects, or other medications.

Keep your peace of mind

Although the COVID-19 vaccine has caused reactions in some people, there’s no need to panic. All the reactions appeared in the vaccine’s trial phase, which means we haven’t run into any surprises. That’s a positive note. It shows that so far, the vaccine is working like scientists predicted. 

For peace of mind about your COVID-19 vaccination, see an allergist. They can help you understand your options for getting vaccinated safely.

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