Some 'anaphylactic' reactions to flu shots may just be stress responses

Some adverse reactions to influenza vaccinations may be safe to de-labeled—that is, deemed safe for further flu vaccinations—from "allergies" to "stress-related responses" because they do not meet the criteria for anaphylaxis, say authors of a research letter published today by the Medical Journal of Australia.

"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 immunization 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.

Carr and colleagues 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%)," they reported.

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

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

The findings suggest that influenza vaccine allergy may be overdiagnosed, as conditions that mimic vaccine anaphylaxis are more common than anaphylaxis itself.

"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."