Even though allergic reactions to vaccines generally are rare—with the incidence of anaphylaxis estimated at 1.31 per 1 million doses given—concerns are heightened because of the national campaign to immunize Americans against COVID-19.

A perspective article in the Annals of Asthma, Allergy and Immunology discusses how to screen for possible allergic reactions and when vaccines should be offered or avoided.

Background information in the article authored by Boys Town National Research Hospital–led researchers notes that recent immediate allergic reactions clinically compatible with anaphylaxis have occurred in recipients of both the Pfizer-BioNTech and Moderna mRNA SARS-CoV-2 (CoV-2 or COVID) vaccines, although specific mechanisms and inciting antigen/agents have not been identified.

The CDC reported adverse reactions from the Pfizer-BioNTech COVID-19 vaccine at a rate of 11.1 cases per million doses. (A later CDC report on the Moderna vaccine found similar rates.)

The CDC has recommended that the mRNA CoV-2 vaccines should not be administered to individuals with a known history of a severe allergic reaction to any component of the vaccine.

The perspective article points out that although the specific vaccine component causing anaphylaxis has not been identified, polyethylene glycol (PEG), one of the ingredients, has been known to cause anaphylaxis in other clinical settings. Furthermore, the authors add, no other vaccines currently use PEG2000, which is a component of both mRNA CoV-2 vaccines.

The authors explain that polysorbate, an excipient found in medications and foods, can cross-react with PEG, adding, “Accordingly, patients with documented allergic reactions to polysorbate should not be immunized with the mRNA vaccines.”

The perspective article points to a recent review that hypothesizes a potential relationship between the lipid-PEG2000 component of the lipid nanoparticle mRNA carrier system and increased risk for anaphylactic reactions.

The CDC advises that vaccine recipients experiencing a severe allergic reaction or an immediate allergic reaction of any severity within 4 hours of receiving the first dose should not receive the second one. The authors of the perspective also advise that anyone experiencing an allergic reaction or having serious questions about their risks should be referred to an allergist/immunologist for evaluation.

While the American College of Allergy, Asthma and Immunology (ACAAI) does not currently endorse any testing protocol for PEG, polysorbate, or the mRNA COVID vaccines, testing protocols exist for those agents. “However, presently there are no established predictive values and safety data for the proposed skin testing procedures,” the authors write.
“In those at higher-risk for developing serious or fatal COVID-19 infections, and who have previously experienced a suspected or confirmed severe allergic reaction to a CoV-2 vaccine or any of its components, a graded vaccine administration protocol could provide an option for administration,” they add. “Guidance for the graded administration of a vaccine has previously been published: administer 0.05 mL 1:10 dilution, 10%, 20%, 30%, and 40% of the full dose incrementally in alternate arms at 15-minute intervals, followed by a minimum 30-minute observation period.”

The article cautions, however, that no data yet confirms efficacy and safety of the approach, which is commonly performed with other vaccines. Until such data are available, the authors add, graded vaccine administration should be considered experimental and is not endorsed by the ACAAI.

On the other hand, the ACAAI COVID-19 Vaccine Task Force recommends that all patients should be screened by asking several questions to determine possible risk for an allergic reaction to the mRNA COVID-19 vaccines. The group emphasizes that a history of food, venom, inhalant, latex, or medication allergy should not preclude patients from receiving the vaccine.

The questions include:
• Do you have a history of a severe allergic reaction to an injectable medication (intravenous, intramuscular, or subcutaneous)?
• Do you have a history of a severe allergic reaction to a prior vaccine?
• Do you have a history of a severe allergic reaction to an injectable or vaccine containing PEG, a polysorbate, or polyoxyl 35 castor oil (e.g., paclitaxel)?

In addition, all patients should have direct observation/waiting time of 15 minutes after vaccination, with the exception of those with a history of systemic reactions to food, drugs, or venoms, who should wait 30 minutes, according to the guidance. Furthermore, as required by public health officials, all facilities administering the vaccine must be prepared to treat anaphylaxis.

The authors urge that caution should be exercised in patients with mast cell–activation disorders/idiopathic anaphylaxis, as risk in that group is not known.

“Thus, the evaluation of at-risk patients should be individualized. As part of that evaluation, one should employ shared decision-making surrounding the approach to testing and future vaccination,” the article concludes. “It is vital that patients understand the overall benefit of vaccination against CoV-2 virus in relationship to the extremely low overall risk of an allergic reaction.”
The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.

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