key: cord-1023843-qxouby53
authors: Jeimy, Samira; Wong, Tiffany; Song, Christine
title: Immediate reactions after mRNA SARS-CoV-2 vaccination
date: 2021-12-06
journal: CMAJ
DOI: 10.1503/cmaj.211581
sha: 563a6d69966d3182df6eb04a247f3ee63f3545f8
doc_id: 1023843
cord_uid: qxouby53

nan

In a retrospective case series of 189 people who reported immediate reactions to the first vaccine dose, a second dose was successfully administered to 159. 2 Nonspecific and single-system reactions (e.g., flushing, hives, lightheadedness) to the first dose were more common than anaphylaxis, 2 and these can be mitigated by counselling and conservative treatment, including second-generation antihistamines.

In a case series of 80 people, 81% of whom had immediate-onset reactions to mRNA vaccines, 18% had positive skin tests to polyethylene glycol (PEG) or to polysorbate-80, which is structurally similar. However, 89% tolerated the second dose, including those with positive skin tests. 4 This argues against the presence of anti-PEG immunoglobulin (Ig) E antibodies.

The mechanism of mRNA vaccine reactions is unknown. Liposomes, like those in the mRNA vaccines, can trigger complement activation-related pseudoallergy, leading to mast cell degranulation. The same mechanism mediates reactions to other liposomal medications, such as liposomal doxorubicin. Pseudoallergy may explain why people with immediate reactions to their first dose are able to tolerate subsequent doses. 5

The National Advisory Committee on Immunizations recommends that people with suspected allergic reactions after a first dose of an mRNA vaccine can receive additional doses of any mRNA vaccine, in consultation with an allergist. Expedited allergist assessments can be conducted in person (https://cirnetwork.ca/sic-network-patient-referrals/) or via an electronic platform (https://otnhub.ca).

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Samira Jeimy MD PhD, Tiffany Wong MD, Christine Song MD n Cite as: CMAJ 2021 December 6;193:E1842. doi: 10.1503/cmaj.211581; early-released November 12, 2021

Reports of anaphylaxis after receipt of mRNA COVID-19 vaccines in the US

Safety evaluation of the second dose of messenger RNA COVID-19 vaccines in patients with immediate reactions to the first dose

Safety of administration of BNT162b2 mRNA (Pfizer-BioNTech) COVID-19 Vaccine in youths and young adults with a history of acute lymphoblastic leukemia and allergy to PEG-asparaginase

First dose mRNA COVID-19 vaccine allergic reactions: limited role for excipient skin testing

Assessment of allergic and anaphylactic reactions to mRNA COVID-19 vaccines with confirmatory testing in a US regional health system

Competing interests: None declared.