Managing suspected allergy to Covid vaccines
The Pfizer Covid mRNA vaccine containing polyethylene glycol (PEG) /macrogol was first administered on the 8th of December. By the end of the day two anaphylactic reactions had been reported in women; one with a history of food anaphylaxis and the other with anaphylactic reactions to multiple classes of drugs. Allergy to PEG was suspected as the cause as there were no other known allergens in the vaccine. Alternative mechanisms postulated included complement activation by the vaccine or non-IgE mediated anaphylaxis.
Severe allergic reactions to the Covid-19 vaccines are rare. Despite raised awareness since the Covid vaccination programme started, only one patient has been described with PEG-induced anaphylaxis following vaccination with an mRNA Covid vaccine. The majority of reactions to the Covid vaccines have not been confirmed as anaphylaxis and we are not aware of anyone with an immediate increase in serum mast cell tryptase.
The BSACI Vaccine Working Group has developed a series of FAQs which should allow first or repeat vaccination in the majority of those presenting to allergy services without the need for detailed allergy investigation. Those, who develop anaphylaxis with objective signs following vaccination should be investigated by skin testing to the vaccines and their excipients in specialised drug allergy units. An algorithm describing the pathway for allergy specialists is shown.
Immediate cutaneous local reactions, cough and metallic taste after vaccination are common and if easily managed with oral antihistamines then the second dose of the same vaccine can be recommended under antihistamine cover. Symptoms that are delayed >2h after vaccination are almost always due to the immunogenic effect of the vaccine and some of these can also be managed with AH cover and patients advised that they may develop similar symptoms with subsequent injections of the same vaccine.
Read our FAQs and share with other health care professionals caring for patients with allergies.
BSACI Standards of Care Committee would like to thank the BSACI Vaccine Allergy Group and Dr Shuaib Nasser for their expertise on the development of these FAQs.
The BSACI VAWG have also designed the below algorithm to help allergy specialists treat patients with a history of Anaphylaxis
This is available to download here