Anaphylaxis found to affect 0.025% of COVID-19 mRNA vaccine recipients

Matt Woodley

10/03/2021 5:08:34 PM

New research utilising real-world data suggests the rate is largely comparable to most antibiotics.

Person receiving an mRNA vaccine.
Anaphylaxis occurred at a rate of 2.47 per 10,000 individuals, and each of those individuals captured by the study made a full recovery. (Image: AAP)

Prior to the COVID-19 pandemic, mRNA-based vaccines had never been used widely in humans.
The revolutionary technology holds many advantages, but also led to concerns over potential unknown short- and long-term side effects.
Reports of deaths among the elderly in Norway who had received the Pfizer/BioNTech mRNA vaccine approved for use in Australia were followed by anecdotal reports it produced anaphylactic reactions at a much higher rate – albeit still low – compared to other widely used vaccines.
However, new research investigating acute allergic reactions to mRNA Pfizer/BioNTech and Moderna COVID vaccines has found they only occur in around 0.025% of people, or 2.47 per 10,000 individuals.
The study was conducted using real-world data taken from vaccinations administered to nearly 53,000 employees at Mass General Brigham in the US.
According to lead author Dr Kimberly Blumenthal, co-director of the Clinical Epidemiology Program at Massachusetts General Hospital, once employee vaccinations began at Mass General Brigham, she and her colleagues set about carefully documenting all allergic reactions, including anaphylaxis.
‘The COVID-19 mRNA vaccines are the first vaccines of their kind, and they have remarkable efficacy and safety across all populations,’ she said.
‘It is critical to have accurate information on allergic reactions to these vaccines, not only for our current situation, but also because this new vaccine platform is so important for future pandemic responses.’
To achieve this, the team analysed employee surveys to estimate the incidence of allergic reactions and used multiple surveillance methods to identify the true incidence of anaphylaxis.
Among the 52,805 employees who were surveyed after receiving their first dose of an mRNA vaccine – including an estimated 4000 with significant allergies to foods and medications – 2% experienced allergic reactions, and anaphylaxis occurred at a rate of 2.47 per 10,000 individuals.
‘To put this in perspective, this is largely comparable to anaphylactic reactions from common antibiotics,’ Dr Blumenthal said.
The investigators noted that although the incidence of anaphylaxis was higher than that estimated by the Centers for Disease Control and Prevention (US CDC) – which put the rate at 0.025–0.11 per 10,000 vaccinations – the overall risk of anaphylaxis post-injection with an mRNA vaccine is still ‘extremely low’ and ‘largely comparable to other common healthcare exposures’.
‘The only allergy exclusion for vaccination was a prior episode of anaphylaxis to an inactive ingredient in the vaccine, called polyethylene glycol, or a cross-reactive inactive ingredient called polysorbate,’ co-senior author Dr Paige Wickner said.
‘Another important aspect of our study is that all of our anaphylaxis cases recovered – no one had anaphylactic shock or required a breathing tube, even temporarily.’
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anaphylaxis coronavirus COVID-19 Moderna mRNA vaccines Pfizer/BioNtech

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