Anaphylaxis in less than 1% of ‘highly allergic’ after Pfizer: Study

Jolyon Attwooll

1/09/2021 4:08:35 PM

The new research finding also suggests a screening questionnaire could be used to enhance patient safety.

A vial of Pfizer and a syringe.
Recent estimates from the US Centres for Disease Control and Prevention suggest anaphylactic reactions after Pfizer occur in just over four per million people. (Image: AAP)

A newly published study has found the vast majority of people who have a prior history of anaphylaxis are unlikely to have a serious adverse reaction after receiving Pfizer’s COVID-19 vaccine.
The research, carried out in the early stages of Israel’s vaccination program, closely monitored 429 ‘highly allergic’ people during and after vaccination and found 98% had no allergic reaction to their first dose.
One per cent had mild allergic responses, and 0.7% (three people in total) had anaphylactic reactions. Nobody in the study required hospitalisation and symptoms resolved within 2–6 hours of treatment.
According to the authors, the research is the first to focus specifically on an immunisation program using Pfizer for highly allergic patients, helping to build on information gathered during clinical trials.
The researchers suggest that the methods used in the study could be transferred to ‘any clinical setting’ to ensure as broad a section of the community as possible is able to be vaccinated against COVID-19, including those deemed highly allergic.
They write that an algorithm used in the study, which included a detailed questionnaire, could help ensure high-risk allergy sufferers are vaccinated in the safest possible setting, while minimising the risk of any long-term damage should an adverse reaction occur.
The overall study looked at patients who attended a vaccination hub at the Sheba Medical Center in Ramat Gan in Israel and used the de-identified data of 8102 patients with allergies.
After an initial assessment, 6883 people – or around 85% of the total cohort – were deemed low-risk and able to receive their vaccination in regular settings.
The remaining 1219 people answered a questionnaire that featured five questions about prior allergic or anaphylactic reactions to drugs or vaccines, other allergies, the treatments used during previous reactions, current use of drugs and other immune comorbidities.
After having their responses assessed by a clinical immunology and allergy team, a further 785 people were defined as low risk, allowing them to be vaccinated in a regular setting.
The remaining 429 people, who were deemed ‘highly allergic’, were still vaccinated, but observation was extended to two hours post-vaccination by a dedicated allergy team.
The study also found that most of those who did not experience an adverse reaction following their first dose did not have a reaction after their second either. Only four mildly allergic reactions were recorded among the 218 individuals who had a follow-up vaccination, with no anaphylaxis.
‘This finding may suggest that a shortened observation period may be sufficient after the second dose of the vaccine for patients who did not experience a reaction to the first dose,’ the authors wrote.
Meanwhile, those vaccinated in a regular setting did not report any adverse reactions, although the authors did note that they were limited in their ability to follow up.
The paper suggests that the methods employed could be useful in vaccination settings around the world when assessing the risks for those with allergies.
‘In this study, we created an algorithm for rapid screening of individuals who were potentially at risk of immediate allergic reaction to the BNT162b2 [Pfizer] vaccine,’ the authors wrote.
‘This simple method can be easily implemented in any country and allowed 95% of applicants to be immunised in the regular settings in Israel.’
However, the authors did note that the study confirmed anaphylactic reactions to Pfizer are higher than for other commonly used vaccines.
A study conducted by the US Centers for Disease Control and Prevention (CDC) in January had similar findings. While the risks remained extremely small, the analysis indicated around 11 per million anaphylactic reactions occurred following Pfizer, an estimate that was later reduced to just over four per million. 
These rates are far lower than those recorded in a study of Mass General Brigham employees earlier this year, which found anaphylaxis affected 0.025% of mRNA vaccine recipients (2.47 per 10,000), including those who received Moderna.
Previous studies indicate the overall rate of anaphylaxis after vaccination more broadly is about 1.3 per million.
The authors of the recent Israeli research said more work is required to confirm the reasons for anaphylaxis among this highly allergic group.
Their analysis did not include any further probing into possible root causes for anaphylaxis but cited previous research suggesting the polyethylene glycol (PEG) ingredient used in the making of the vaccine could be a possible candidate.
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