21 anaphylaxis cases to first Pfizer-BioNTech coronavirus vaccine out of more than 1.8 million jabs, study suggests

Alexandra Thompson
·4-min read
Illustrative picture of coronavirus vaccine under trail
Like all vaccines, the Pfizer-BioNTech coronavirus jab can cause allergic reactions in rare cases. COVID-19 is the name of the disease triggered by the infection. (Stock, Getty Images)

Just 21 anaphylaxis cases are confirmed to have arisen after more than 1.8 million first doses of the Pfizer-BioNTech coronavirus vaccine were administered in the US.

Two NHS workers developed an anaphylactoid reaction – typically a mild rash, breathlessness and sometimes a decline in blood pressure – the day the much-anticipated jab was rolled out in the UK.

This prompted the UK’s vaccine regulator to warn anyone with a “history of significant allergic reactions” should bypass the jab.

None of the 21 patients died, with the vast majority (81%) already known to react to allergens like tropical fruit, bee stings and penicillin.

Anaphylaxis is a life-threatening allergic reaction that rarely occurs after a vaccine, with the regulator stressing its warning was a precautionary measure.

To better understand the extent of the issue, scientists from the US Centers for Disease Control and Prevention (CDC) analysed reports of suspected severe allergic reactions and anaphylaxis following immunisation that were submitted to the Vaccine Adverse Event Reporting System (VAERS).

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Between 14 and 23 December, when more than 1.8 million first dose Pfizer-BioNTech jabs had been administered, just 21 anaphylaxis case reports had come to light.

This equates to an estimated 11.1 incidents per 1 million doses. For comparison, flu vaccines are said to cause 1.3 anaphylaxis cases per 1 million people, with both incidents being “exceedingly rare”.

Of the 21 cases, hives were a common side effect. (Stock, Getty Images)
Of the 21 cases, hives were a common side effect. (Stock, Getty Images)

The CDC doctors analysed the VAERS reports to ensure they met the Brighton Collaboration anaphylaxis criteria; defined as the rapid onset and progression of symptoms affecting two or more organs.

Reactions that occurred more than a day after the jab was administered were excluded “because of the difficulty in clearly attributing allergic reactions with delayed onset after vaccination”.

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The Moderna coronavirus vaccine, which has a similar mode of action to the Pfizer-BioNTech jab, was only available in the US from 21 December, prompting the scientists to focus just on the latter shot.

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Four of the 21 patients (19%) were hospitalised, three in intensive care, while 17 (81%) were treated in an emergency department.

All but one (95%) are known to have been discharged or recovered by the time their report reached the VAERS, with the last case being “not specified”.

“No deaths from anaphylaxis were reported,” the scientists wrote in the journal JAMA.

Just over seven in 10 (71%) of the patients experienced anaphylaxis symptoms within 15 minutes of being vaccinated, with the most common signs including hives, face swelling and a sense their throat was closing.

More than four in five had a “documented history of allergies or allergic reactions”.

A third (33%) had experienced anaphylaxis before, of whom one endured the event after a rabies vaccine and another following a flu jab.

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During the same study period, 83 non-anaphylaxis allergic reactions were reported to the VAERS.

Stressing the importance of vaccines, the scientists wrote: “Mortality from COVID-19 [the disease caused by the coronavirus] in populations at high risk is substantial and treatment options are limited.

“Widespread vaccination against COVID-19 with highly effective vaccines represents an important tool in efforts to control the pandemic.”

Nevertheless, vaccine centres should have supplies to manage anaphylaxis, with patients also being monitored for up to half an hour after the jab, they added.

Dr Nancy Messonnier, from the CDC, previously said 1.3 anaphylaxis cases occur after a flu vaccination per 1 million people.

While the side effect appears to be higher following a coronavirus jab, she stressed the reaction is “still exceedingly rare”.

Research has previously revealed less than 1% of people who received the Pfizer-BioNTech vaccine in a late-stage study developed an allergic reaction, which did not stop regulators granting approval.

Experts have previously stressed the risk has to be “put into perspective”, with similar side effects occurring every year with the seasonal flu vaccine and even Marmite having the potential to trigger allergies.

Allergies aside, the study that led to the jab’s UK approval reported the “incidence of serious adverse events was low and was similar in the vaccine and placebo groups”.

“Few” participants in either group dropped out of the trial due to intolerable or dangerous side effects.

In addition, “no deaths were considered by the investigators to be related to the vaccine or placebo”.

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