Published: 3 June 2021


Anaphylaxis following vaccination: focus on Comirnaty

Published: 3 June 2021
Prescriber Update 42(2): 18–20
June 2021

Key Messages

  • Anaphylaxis is a very rare adverse event that may occur following administration of any vaccine, including vaccines for COVID-19 infection, such as Comirnaty.
  • COVID-19 vaccines must always be administered in a setting where anaphylaxis can be promptly identified and treated.
  • Anyone receiving the Comirnaty vaccine should be closely observed for at least 20 minutes following vaccination, but individuals with risk factors for anaphylaxis should be observed for a minimum of 30 minutes.
  • Intramuscular adrenaline is the first line treatment for anaphylaxis.
  • 1:1000 adrenaline must be readily available at vaccination centres.
  • Individuals should not receive Comirnaty if they have a history of allergic reactions to any of the vaccine ingredients or if they experience anaphylaxis after the first dose.

Anaphylaxis is a life-threatening allergic reaction that can occur very rarely following the administration of a vaccine.1

The New Zealand roll-out of COVID-19 vaccines commenced on 20 February 2021. The vaccine currently available is Pfizer/BioNTech mRNA COVID-19 vaccine (Comirnaty). There have been reports of suspected anaphylaxis after administration of the Comirnaty vaccine in New Zealand.2

It is essential that vaccinators administering COVID-19 vaccines can promptly identify and provide emergency treatment for anaphylaxis.


Anaphylaxis is a severe, life-threatening, acute hypersensitivity reaction characterised by:

  • rapidly evolving airway compromise due to pharyngeal or laryngeal oedema
  • and/or wheeze and increased work of breathing due to bronchospasm
  • and/or circulatory effects, such as hypotension and/or tachycardia.

Although not always seen, most cases are associated with skin and mucosal changes (eg, flushing, hives or welts, swelling of lips, face and eyes).3–6 People sometimes report perioral numbness/tingling as a first sign of anaphylaxis. It is very important to start treatment if anaphylaxis is suspected, even if these signs are not observed.

Anaphylaxis results from the sudden degranulation of mast cells and basophils, releasing mediators such as histamine, proteases, prostaglandins and leukotrienes into the circulation.7,8

Risk factors for anaphylaxis to Comirnaty vaccine

Individuals should not receive the Comirnaty vaccine if they have a history of anaphylaxis to any of the ingredients in the vaccine.1,9,10 The vaccine ingredients are listed in the New Zealand data sheet (see section 2 for the active ingredient and section 6.1 for the list of excipients).9

Polyethylene glycol (PEG), also known as macrogol, is an ingredient in mRNA COVID-19 vaccines. PEG is present in many different types of medicines and is recognised as an allergen that can trigger anaphylaxis in some people.1,10–13

Individuals with a history of an anaphylaxis-type reaction to any other substance have an increased risk of an anaphylactic response to mRNA COVID-19 vaccines.10 These individuals can still receive the vaccine but should be observed for a minimum of 30 minutes and be given clear advice on symptoms of anaphylaxis and how to call for help, before leaving the vaccination facility.10

Treatment of anaphylaxis

Adrenaline is the first-line treatment for anaphylaxis and should be given without delay as soon as anaphylaxis is suspected.6,14,15

1:1000 adrenaline must always be readily available at vaccination centres.

Adrenaline should be administered by deep intramuscular injection into the outer thigh. Most adults should receive 0.5 mg as an initial dose (0.5 mL of 1:1000 adrenaline). If it is known or suspected that the individual weighs less than 50 kg, the dose can be reduced using 0.01 mL/kg of 1:1000 adrenaline up to a maximum of 0.5 mL per dose. The dose can be repeated every five minutes as required until definitive help arrives.14

All cases of anaphylaxis should be admitted to hospital for observation.6,14,15

Tests to confirm anaphylaxis

Mast cell tryptase is a highly specific but insensitive marker for anaphylaxis.3 Tryptase levels are elevated from 15 minutes to 3 hours after the onset of anaphylaxis.16,17

Blood samples taken up to 4–6 hours from onset may still show an elevated tryptase level.3,5 A further sample taken more than 24 hours after resolution of symptoms should be obtained as a baseline measure.

An acute serum tryptase level greater or equal to 2 µg/L + (1.2 x baseline level) supports the diagnosis of anaphylaxis.16,17

Recording and reporting of anaphylaxis following Comirnaty vaccination

Following the immediate emergency management of the patient and arranging transfer to hospital, the anaphylaxis event should be documented in the COVID-19 Immunisation Register (CIR). Adverse events following immunisation (AEFIs) that occur after the person has left the vaccination centre should be reported to the Centre for Adverse Reactions Monitoring (CARM) using the online form. It is important to include as much detail as possible in the description of the suspected anaphylaxis event, including symptoms, signs, time of onset and response to treatment. Reports of suspected anaphylaxis will be assessed by CARM against the Brighton Collaboration case definition for anaphylaxis.18

Implications of anaphylaxis for further vaccination

Individuals who experience anaphylaxis to the first dose of Comirnaty should not receive further doses of the vaccine.1,9,10


  1. Australasian Society of Clinical Immunology and Allergy (ASCIA). 2021. Allergy, Immunodeficiency, Autoimmunity and COVID-19 Vaccination Position Statement, 14 April 2021. URL: (accessed 19 April 2021).
  2. Medsafe. 2021. Safety report #5 – 3 April 2021 published 5 May 2021. URL: (accessed 5 May 2021).
  3. Safety Platform for Emergency vACcines (SPEAC). 2021. SO2- D2.5.2.1 – AESI Case Definition Companion Guide for 1st Tier AESI: Anaphylaxis. URL: (accessed 19 April 2021).
  4. Rüggeberg JU, Gold MS, Bayas J-M, et al. 2007. Anaphylaxis: case definition and guidelines for data collection, analysis, and presentation of immunization safety data. Vaccine 25(31): 5675–84. DOI: (accessed 19 April 2021).
  5. National Institute for Health and Care Excellence (NICE). 2020. Anaphylaxis: Assessment and referral after emergency treatment. Clinical guideline [CG134], 14 December 2011 (last updated 24 August 2020). URL: (accessed 19 April 2021).
  6. Australasian Society of Clinical Immunology and Allergy (ASCIA). 2020. ASCIA Guidelines – Acute Management of Anaphylaxis. URL: (accessed 19 April 2021).
  7. Kemp SF. 2019. Pathophysiology of anaphylaxis. In: UpToDate 31 October 2019. URL: (accessed 21 April 2021).
  8. Castells MC and Phillips EJ. 2020. Maintaining safety with SARS-CoV-2 vaccines. New England Journal of Medicine 384(7): 643-9. DOI: 10.1056/NEJMra2035343 (accessed 21 April 2021).
  9. Pfizer New Zealand Ltd. 2021. Comirnaty COVID-19 vaccine New Zealand Data Sheet 6 April 2021. URL: (accessed 21 April 2021).
  10. Immunisation Advisory Centre (IMAC). 2021. COVID-19 vaccinator information March 2021. URL: (accessed 19 April 2021).
  11. Garvey LH and Nasser S. 2021. Anaphylaxis to the first COVID-19 vaccine: is polyethylene glycol (PEG) the culprit? British Journal of Anaesthesia 126(3): e106–8. DOI: (accessed 19 April 2021).
  12. Sellaturay P, Nasser S, Islam S, et al. 2021. Polyethylene glycol (PEG) is a cause of anaphylaxis to the Pfizer/BioNTech mRNA COVID-19 vaccine. Clinical & Experimental Allergy 00:1–3. DOI: (accessed 20 April 2021).
  13. Stone CA, Liu Y, Relling MV, et al. 2019. Immediate hypersensitivity to polyethylene glycols and polysorbates: more common than we have recognized. The Journal of Allergy and Clinical Immunology: In Practice 7(5): 1533–1540.e8. DOI: (accessed 20 April 2021).
  14. New Zealand Resuscitation Council. 2019. Anaphylaxis January 2019. URL: (accessed 19 April 2021).
  15. Ministry of Health. 2020. Immunisation Handbook 2020: Anaphylaxis response/management 25 September 2020. URL: (accessed 19 April 2021).
  16. Kelso JM. 2020. Anaphylaxis: confirming the diagnosis and determining the cause(s). In: UpToDate 28 July 2020. URL: (accessed 21 April 2021).
  17. Cardona V, Ansotegui IJ, Ebisawa M, et al. 2020. World Allergy Organization anaphylaxis guidance 2020. World Allergy Organization Journal 13(10): 100472. DOI: (accessed 19 April 2021).
  18. Brighton Collaboration. 2021. Brighton Collaboration Case Definitions. URL: (accessed 19 April 2021).
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