Allergies to flu vaccine appear overdiagnosed

The small Australian study suggests many patients unnecessarily avoid these valuable vaccines.

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Patients are often incorrectly diagnosed with allergies to influenza vaccines, research from Monash Health suggests.  

Researchers found that none of the 49 adults referred to their allergy clinic with anaphylaxis to the flu vaccines met the criteria for anaphylaxis when challenged.  

“Our findings suggest that influenza vaccine allergy may be over-diagnosed,” the authors said. 

Dr Kerry Hancock, chair of the RACGP’s Respiratory Medicine Specific Interests network, said the findings were reassuring. 

“It implies that a lot of these patients of ours who think that they’ve had significant reactions to influenza vaccines may not have had anaphylaxis,” she told The Medical Republic. 

To better understand the true rate of anaphylaxis to influenza vaccine, the researchers reviewed the records of all the adults diagnosed with influenza vaccine allergies who attended the Monash Health adult vaccine allergy service over a six-month period.  

Only seven of these 49 patients met the criteria for anaphylaxis in their initial reaction, the researchers said.  

Dermatologic symptoms accounted for more than two thirds of reactions. Respiratory symptoms accounted for more than half, and these included reactions such as observed hives or urticaria, hypoxia and hypotension.  

But when the patients, who were mainly female attendees, were challenged with influenza vaccines, none met the criteria for anaphylaxis. 

Nevertheless, 20 had an immunisation stress-related response, one in six had pruritus, one in seven had a sensation in their throat or dyspnoea, one in eight had a rash or generalised flushing, one in 12 had localised tingling and one in 16 had gastrointestinal symptoms.  

The clinicians were able to remove the “allergy” label from 13 patients immediately thanks to their mild symptoms, and over the course of the following year and another challenge with a different vaccine, the remainder of the patients were de-labelled. 

The authors urged those patients with a reaction to be “promptly” referred to an allergist for assessment, citing figures that showed only around one in one million doses of vaccine was thought to be linked to anaphylaxis. In contrast, 4-7% of doses were affected by a stress response, they said.  

“It will probably be safe to de-label many patients because their reactions do not meet anaphylaxis criteria,” they wrote.   

But Dr Hancock said it would be difficult to ensure these patients were seen by an allergist.  

“It’s incredibly difficult to access allergy specialists, so that’s going to be the significant barrier,” she said. 

Nevertheless, she said it was worth initiating the process for patients to have their label challenged, even if it took months or a year. 

“Let’s find these patients who’ve been labelled anaphylactic and get them into the allergy clinics in preparation for next flu season.”   

Some patients were hesitant to be vaccinated after having had an unpleasant experience, said Dr Hancock.  

“And they are getting older and putting themselves at risk. That group of patients are often very hard to shift in their thinking about the influenza vaccine.” 

One step would be to determine how the allergy label originated, she said. This could involve digging into specific symptoms, such as asking patients if they had hives, nausea or muscle aches.  

“If their symptoms don’t meet the criteria for allergy, you would probably feel reasonably safe in saying, ‘Well, that doesn’t seem to be an anaphylactic reaction, are you prepared to have an influenza vaccine?’” 

The researchers also suggested the challenge approach could be “cautiously applied” to other vaccines, including those for covid. 

MJA 2022, online 4 July