Some flu vaccine reactions could be misdiagnosed as anaphylaxis

Some adverse reactions to influenza vaccinations could be stress-related responses being misdiagnosed as anaphylaxis, according to authors of a research letter published by the Medical Journal of Australia.

The researchers reviewed the clinical records of all adults (18 years or older) with diagnoses of influenza vaccine allergies who attended the Monash Health adult vaccine allergy service during 1 April 2017–31 August 2021.

“The index reactions of seven of the 49 participants met the Brighton criteria for anaphylaxis; the most frequent symptoms were dermatologic (70%) or respiratory reactions (57%),” the researchers reported.

“Following split dose (10 participants) or full dose challenges (39 participants), 20 people had symptoms consistent with immunisation stress-related responses, but none met the Brighton criteria for anaphylaxis.

“Thirteen of the 20 were de-labelled because their symptoms were mild; the other seven were also de-labelled after challenge with a different influenza vaccine the following year.”

“As it can be difficult to distinguish influenza vaccine-associated anaphylaxis — estimated by one American study to affect 1.35 people per one million doses — from the more numerous immunisation stress-related responses — affecting 4–7% of influenza vaccine recipients — the latter may be misdiagnosed as allergies,” wrote the authors, led by Dr Beau Carr, from Monash Health.

“Distinguishing between anaphylaxis and an acute stress response in acute health care is difficult, despite World Health Organization guidance,” Carr and colleagues concluded.

“We recommend that reactions be treated as allergic if clinically suspected, but also that the patient be promptly referred to an allergist for further assessment. It will probably be safe to de-label many patients because their reactions do not meet anaphylaxis criteria.”

Image credit: ©stock.adobe.com/au/ThamKC