Skip to main content
myths vs facts

Vaccines for COVID-19: Why are some Canadians allergic to the truth?

On some future earth a horrible disease threatens to destroy humanity. Against all odds, scientists find a cure! Even more improbably they mass produce the cure. The treatment proves safe and effective and the planet is saved…until 20% of the world’s people develop idiosyncratic beliefs and decline to take the cure. The disease surges back and becomes an ongoing scourge. 

This is not science-fiction, this is Canada in 2021. The truth of the vaccines is they are miraculous = 95% effective at preventing COVID-19 infection. They reduce the risk of bad outcomes enormously. Of all patients hospitalized with COVID-19 in Ontario, fewer than 4% were fully vaccinated! In contrast, over 92% of hospitalized people were unvaccinated. You do the math- vaccines work!

screenshot of tweet with text and graphs

Despite amazing effectiveness in the prevention of COVID-19, COVID-19 hospitalization and COVID-19 death, only 76.6% of eligible Canadians are vaccinated. Many vaccine-hesitant people (and most antivaxxers) believe and propagate the idea that vaccines don’t work and/or are fraught with side effects like allergic reactions. These dangerous ideas lead to dangerous behaviours (e.g. choosing to remain unvaccinated in a pandemic). Such dangerous ideas are called cognogens, and have been well discussed in this blog. It turns out ill-founded ideas can be lethal as viruses!

One of our talented chief residents addressed a dangerous COVID-19 cognogen, the idea that allergic reactions are common with COVID-19 vaccines. She took on the false idea that allergies put many people who require vaccination, especially people with some history of allergic disease, at risk. This is a critical discussion since concerned and angry patients are flooding our allergists with requests for vaccine exemptions. Dr. Eman Badawod gave an amazing Medical Grand Rounds that summarized the science showing allergies are actually very rare with COVID-19 vaccines and no fatalities have occurred from vaccine allergy (see Tweet graphic below). With input from Dr. Anne Ellis, Chair of Allergy and Immunology, Dr. Badawod summarized the facts. I asked her to write this guest blog because our allergists are being swamped with requests for allergy testing and vaccine exemptions from patients with many inflated ideas of allergy risk, driven by social media. The general tone from social media is that allergies merit vaccine exemptions (they don’t) and that vaccines often cause dangerous allergic reactions (they are rare). The resulting patient exchanges with our doctors have often been uncivil, especially when faculty attempt to put the risk of allergy in proper perspective. It’s time to air the facts.

screenshot tweet of masked doctor giving a presentation

Please enjoy this balanced, evidence-based, discussion of the true (low) risk of allergic reactions to COVID-19 Vaccines in a guest blog by Dr. Eman Badawod and Dr. Anne Ellis.


Guest blog:

Vaccines have saved more lives in the past 50 years in Canada than any other health intervention (1). One hundred years ago infectious diseases were the leading cause of death worldwide whereas currently they cause less than 5% of all deaths (2). Non-allergic reactions to vaccines are far more common than allergic reactions. In fact, the most common reactions following vaccinations are local reactions and non-immediate skin eruptions (3). True allergic reactions to vaccines are rare. In a large population-based study the rate of allergic reactions following vaccinations was found to be 1.31 cases per million vaccine doses (95% CI, 0.90 – 1.84), with no fatalities reported (4). Despite being very uncommon, the perception of allergy risk contributes to public fearfulness and potentially lead to loss of confidence in vaccine safety.

Vaccines are generally made of two main components: an active component that includes an organism, part of an organism or a toxin that is responsible for inducing an immune response. In this case of the COVID-19 vaccines the active ingredient is a messenger RNA molecule. These active components are rarely the cause of allergic reactions. The other constituents, so-called inactive components, are usually responsible for allergic reactions. These inactive components (excipients) are added to enhance the immune response, prevent bacterial contamination or stabilize the vaccine during transport and storage.

Vaccine allergic reactions classified using the Gell and Coomb’s classification of hypersensitivity reactions.


It is important to distinguish acute onset IgE-mediated reactions from all other allergic reactions because they can manifest as life threatening anaphylaxis. Delayed reactions are often self-limiting, and they’re not usually considered a reason not to receive future doses of the same vaccine.

Another important consideration is allergic mimickers such as vasovagal syncope (fainting) and local reactions. Fainting in response to a needle is common and is unrelated to allergy. Patients feel warm, flushed, nauseated, sweaty and may “pass out”. This faint (aka vasovagal syncope) is not an allergy. It has everything to do with fear and anxiety and nothing to do with vaccine content or allergy (see Table below). Local and systemic effects of vaccine, also not allergic in origin, are listed in the table below (fever chills, pain at the site of injection etc.).

Common non-allergic reactions to vaccines

table of non allergic reactions to vaccines

Two main vaccines using mRNA were developed to prevent COVID-19 infections, Pfizer (BNT16b2) and Moderna (mRNA- 1273). It’s not yet clear if the active ingredient (mRNA) is responsible for inducing allergic reactions or if allergy is related to inactive ingredients. The only inactive ingredient available for skin testing (used to identify if one is allergic to a vaccine component) is Polyethylene glycol (PEG); however the sensitivity and negative predictive values of the PEG skin testing remain unknown (5). PEG is added to different drugs to improve water solubility, but it has not previously been used in vaccines. PEG is added for the purpose of stabilizing the mRNA-containing lipid nanoparticles. On the other hand, Polysorbate 80 has been used in vaccines in the past and has been identified as a rare cause for allergic reactions to vaccines (6). PEG and Polysorbate are structurally similar with polyether domains, raising a concern for cross reactivity. 

Components of COVID-19 mRNA vaccines

table listing components of mRNA vaccineschemistry make up of Pfizer vaccine

After the first day of administration of the Pfizer vaccine in the UK, three allergic reactions were reported. Two of these were consistent with anaphylaxis and occurred within minutes of administration of the vaccine. Both cases responded well to epinephrine. Both patients had a history of allergies (food and drugs). The third reported case was less severe and resolved spontaneously. Anaphylaxis is the most severe form of allergy and can be fatal if untreated. Fortunately, as in these cases, it occurs very quickly (within minutes after the vaccine) while patients are still being monitored and thus can be successfully treated.

In a review of reactions reported to mRNA vaccines in the US from December 14th to the 23rd, 2020 the rate of allergic reactions was 11.1 cases per million doses administered. Eighty-one of these patients had prior documented allergies. The median time of symptom onset was 13 minutes. No deaths from anaphylaxis were reported (7). In Canada, the incidence of anaphylaxis following mRNA vaccines is currently estimated at 7.91 cases per million doses administered. Again, there have been no fatalities or long-term morbidity with these events (8).

So what to do if you are a patient with a history of allergies? The Canadian Society of Allergy and Clinical Immunology (CSACI) recommends proceeding with COVID-19 vaccination with no assessment by an allergist for individuals with history of allergic conditions (including anaphylaxis to food, venom, medications, radiocontrast media or unrelated vaccines). Consultation with an Allergist assessment is also not required for individuals who experienced mild, localized, reactions to prior doses of COVID-19 vaccines or any vaccine components.

An Allergist assessment is only required for individuals who experienced ANAPHYLAXIS following the first dose of a COVID-19 vaccine. Even for these individuals, re-vaccination with the same vaccine, under the supervision of an allergist with a prolonged observations period (30 minutes) ± graded dosing is safe and well tolerated.

To date, there have been more than 250 billion reported cases of COVID-19 worldwide and over 5 million deaths. COVID-19 is dangerous! By comparison, while over 7.3 billion COVID-19 vaccine doses have been administered, to date, there has been no reported fatalities or long-term morbidity associated with allergic reactions or anaphylaxis following COVID-19 vaccine administration. Vaccines are safe and effective!

Given the low mortality of anaphylaxis in general (less than 0.5% in general) and the high morbidity/mortality of COVID-19, the risk of withholding SARS-CoV-2 vaccination exceeds the risk of a severe allergic reactions (9).




3. Shavit R, Maoz-Segal R, Iancovici-Kidon M, Offengenden I, Haj Yahia S, Machnes Maayan D, Lifshitz-Tunitsky Y, Niznik S, Frizinsky S, Deutch M, Elbaz E, Genaim H, Rahav G, Levy I, Belkin A, Regev-Yochay G, Afek A, Agmon-Levin N. Prevalence of Allergic Reactions After Pfizer-BioNTech COVID-19 Vaccination Among Adults With High Allergy Risk. JAMA Netw Open. 2021 Aug 2;4(8):e2122255. doi: 10.1001/jamanetworkopen.2021.22255. PMID: 34463744; PMCID: PMC8408666.

4. McNeil MM, DeStefano F. Vaccine-associated hypersensitivity. J Allergy Clin Immunol. 2018;141(2):463-472. doi:10.1016/j.jaci.2017.12.971

5. Stone BD. PEG skin testing for COVID-19 vaccine allergy. J Allergy Clin Immunol Pract. 2021;9(4):1765. doi:10.1016/j.jaip.2021.02.016

6. Banerji A, Wickner PG, Saff R, Stone CA Jr, Robinson LB, Long AA, Wolfson AR, Williams P, Khan DA, Phillips E, Blumenthal KG. mRNA Vaccines to Prevent COVID-19 Disease and Reported Allergic Reactions: Current Evidence and Suggested Approach. J Allergy Clin Immunol Pract. 2021 Apr;9(4):1423-1437. doi: 10.1016/j.jaip.2020.12.047. Epub 2020 Dec 31. PMID: 33388478; PMCID: PMC7948517.

7. Shimabukuro T, Nair N. Allergic Reactions Including Anaphylaxis After Receipt of the First Dose of Pfizer-BioNTech COVID-19 Vaccine. 2021;325(8):780–781. doi:10.1001/jama.2021.0600

8. Greenhawt M, Abrams EM, Shaker M, Chu DK, Khan D, Akin C, et al. The Risk of Allergic Reaction to SARS-CoV-2 Vaccines and Recommended Evaluation and Management: A Systematic Review, Meta-Analysis, GRADE Assessment, and International Consensus Approach. J allergy Clin Immunol Pract. 2021


Bottom line: Vaccines prevent COVID-19 effectively and reduce hospitalization and death. Vaccines rarely cause allergic reactions. Only if you had anaphylaxis to dose-1 of a COVID-19 vaccine or have a severe, known, allergy to a vaccine constituent do you need to see an allergist. The crazy cognogens that COVID-19 vaccines causes many, dangerous allergic reactions needs to be dispelled.