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What Can Cause A Vaccine Allergy?

Vaccinations provide salvation from a number of diseases. However, sometimes vaccines themselves provoke an undesirable reaction. And often it manifests itself in the form of allergies, but not only her.

The most common consequences of vaccination are mild allergic reactions. By the way, as the number of vaccinations given to people increases over the years, such reactions have also become more common. 

Severe responses to vaccines, such as anaphylaxis, are rare. On average, their risk is estimated at one in a million. Some vaccines, such as the human papillomavirus vaccine, have an even lower rate of severe reactions – about one case per 1.7 million doses. 

However, rates of severe reactions after vaccination can sometimes be higher. For example, at the end of December 2020, a number of deaths were caused by a number of deaths after the introduction of the Covid-19 vaccine in the United States.

The U.S. health agency said allergic reactions to available coronavirus vaccines (Pfizer Inc and Moderna Inc) occur at a rate of 11.1 per 1 million vaccinations. Whereas, for example, influenza vaccines lead to anaphylaxis in about 1.3 cases per million doses.

Also, the US Centers for Disease Control and Prevention has urged those who have a serious reaction to the first dose of the coronavirus vaccine or other vaccines to refuse the second dose. This also applies to people who have already had coronavirus. Recent practice has shown that they can also tolerate COVID-19 vaccination poorly.

It is also recommended not to get vaccinated for people with an allergic reaction to polyethylene glycol (PEG), which is a member of the polysorbate group. This is a group of substances that are used in the cosmetic and pharmaceutical industries as emulsifiers.

Vaccines, in particular the vaccine against COVID-19, contain PEG.


The reasons for allergic reactions to vaccines lie in their composition. In the case of COVID-19 vaccinations, the aforementioned PEG is believed to be the culprit for the allergy. This polyester compound is widely used not only in the pharmaceutical, but also in the cosmetic and food industries.

However, other components of vaccines can also act as causes of hypersensitivity. For example, these are the same antigens that are the main component of the vaccine, preservatives, antibiotics, conjugation agents, stabilizers, adjuvants and media in which the components of the vaccine were cultivated. This list may also contain substances that were inadvertently injected during the vaccination process.

And here a separate place is occupied by proteins, the components of which are gelatin, yeast and substances obtained from eggs. And also – antibiotics, which can also be part of the vaccine. Traditionally and for many years one of the most common causes of allergic reactions to vaccines have been eggs and gelatin, which are used in vaccines. However, the amount of this component in the latest vaccines is microscopically small. 

Let’s take a quick look at some of the ingredients in vaccines that can cause allergies.


Stabilizers are used to protect vaccines from adverse conditions such as excessive heat or freeze-drying processes. The following can act as stabilizers:

– carbohydrates (sucrose and lactose)

– amino acids (monosodium salt of glutamic acid or glycine)

– protein (gelatin or human serum albumin).

For example, gelatin is used as a stabilizer in attenuated vaccinated vaccines. These include, for example, the Japanese encephalitis virus, varicella-zoster virus and MMR vaccine. The latter is a combination vaccine against rubella, measles and mumps. Gelatin causes more allergic reactions than other components of the vaccine. After the introduction of non-gelatinous vaccines in Japan, the incidence of allergies to them dropped sharply.

And the absence of a food reaction to gelatin does not guarantee that you will not have a reaction, including a severe one, to a vaccine with it. Therefore, if you suspect you have a sensitivity to gelatin, or, even more so, if it is clinically proven, before the future vaccination, it is better to do a skin test or a molecular test for the presence of IgE to gelatin again.

But even a confirmed allergy to gelatin does not mean that vaccination is impossible. A positive test result only increases safety precautions. It means that the vaccine should be administered in graduated doses. And after each injection, stay under the supervision of a doctor for some time.


Preservatives such as 2-phenoxyethanol and thimerosal are often added to vaccines to prevent the growth of microorganisms. Thimerosal is a neurotoxic organic mercury compound (50% mercury by mass), however, low concentrations of thimerosal in vaccines are said to result in no adverse reactions.

However, the U.S. Health Service and the American Academy of Pediatrics (AAP) have called for the removal of thimerosal from vaccines that were routinely used in infants prior to 1999. So, with the exception of a few, in American vaccines, thimerosal has been completely removed or reduced to the residual amount (traces) in vaccines for children.

Antimicrobial agents

Antibiotics are used to prevent contamination in vaccine production. Therefore, some vaccines may contain trace amounts of neomycin, polymyxin B, or streptomycin.

However, there are few reports of allergy to antibiotics in vaccines. In the overwhelming majority of cases, reactions of the IV, delayed type are recorded. For example, a papule at the injection site. It can occur within 48 to 96 hours after vaccination. However, if you have had a case of anaphylaxis for a particular type of antibiotic, it is best not to get vaccinated with it.

Yeast proteins

Vaccines against human papillomavirus and hepatitis B are created using antigens from the culture of recombinant baker’s yeast Saccharomyces cerevisiae . Therefore, such preparations contain a little yeast protein (up to 5%). 

However, it is believed that yeast proteins rarely cause allergic reactions to vaccines. However, the doctor or patient has concerns about the occurrence of this type of allergy, it is necessary to conduct a molecular test and check the patient’s hypersensitization to yeast. In case of a positive result, the vaccine should be administered in graduated doses and under constant medical supervision after its administration.


Stubborn nodules that are palpable at the injection site may be a sign of adjuvants such as aluminum salt in the vaccine. To enhance the immune response, such compounds are often added to vaccines.


Vaccination can trigger a latex reaction. This allergen is a potential cause of anaphylaxis. However, today only one case of such an allergy is known.

Egg white

Small amounts of egg white are also found in yellow fever and flu vaccines. In particular, the anti-influenza vaccine is grown in allantoid liquid in the embryos of chicken eggs and contains from 0.2 to 42 μg / ml of egg white. In theory, such a vaccination can cause systemic reactions when the drug is administered to patients who are allergic to egg proteins. But a recent 28 studies reported that more than 4,300 people with egg hypersensitivity did not develop serious reactions (including hypotension and respiratory distress) while receiving flu shots. A small percentage of patients had mild urticaria and mild wheezing. However, now an allergy to egg whites is not a contraindication to a flu shot, but people like everyone else should be under medical supervision for 30 minutes after the injection.

In chick embryos, the yellow fever vaccine is also grown. It may also contain residual egg white. If the skin test result for this vaccine is positive, vaccination should be carried out with a gradually increasing dose and only under medical supervision. If the result is negative, an injection is given with the usual dosage of the drug. But at the same time, the patient must remain in the hospital for the next 30 minutes.

The list of vaccine components that can cause hypersensitivity reactions is constantly updated and is available on the website of the Vaccine Safety Institute:


In the case of COVID-19 vaccines, most of the unwanted symptoms (71%) appeared within 15 minutes after vaccination.

This is the typical time period for type I hypersensitivity reactions. The reaction in this case is due to the interaction of IgE antibodies and a certain component of the vaccine.

Immediate reactions, as usual, appear a few minutes after exposure to the corresponding allergen. As a rule, the maximum manifestation time, although there are exceptions, is 4 hours.

The most common symptoms of type IgE reactions are:   

· angiootok      

· Hives.      

Not so often there are:

· Cough      

· Nasal congestion,      

· Wheezing,      

· Shortness of breath,      

· Diarrhea,      

· Vomiting,      

Abdominal pain      

· Hypotension.      


But at the same time, in children and adolescents, the average rate of occurrence of type I reactions is 0.22 per 100 thousand vaccinations.

Sometimes anaphylactic shock, a severe systemic allergic reaction, can also occur. The reported incidence of potential anaphylaxis after vaccination is 0.065 cases per 100,000 vaccinations given.

It has also been reported that the manifestations of type IV hypersensitivity reactions may be delayed. But this type of reaction is generally considered harmless. They usually begin 48 hours after vaccination and peak between 72 and 96 hours.

Symptoms of such reactions can be observed after the administration of vaccines containing thimerosal, aluminum and antimicrobial agents. The occurrence of such an event is not a contraindication for further vaccinations. And type IV reactions are becoming less common as mercury is removed from modern vaccines.

Another well-known vaccine hypersensitivity reaction is erythema multiforme. This reaction is triggered by several components of the vaccine and can be quite severe in children. 

Another part of the delayed reactions are classified as type III hypersensitivity and are mainly explained by the formation of immune complexes with the involvement of T-lymphocytes.

The most common evidence of a delayed allergic response is a rash. It, in particular, can manifest itself in the form of the already mentioned erythema multiforme, maculopapular eruptions or urticaria. In combination with the latter, as a rule, angioedema is also manifested. It is possible that it will be combined with erythema multiforme. Occasionally arthralgia appears, arthritis worsens, Shenlein-Henoch purpura, joint swelling, and serum sickness occur. In addition to them, renal, hematological and gastrointestinal symptoms are occasionally manifested. 

However, the delayed response of the organism is not always immunologically mediated. In particular, persistent subcutaneous hardening at the injection site can be caused by irritation. As already mentioned, it is caused by adjuvants, which include aluminum. Therefore, it may not be immune hypersensitivity to vaccine constituents.

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