Less than 1% of people who received Pfizer-BioNTech’s coronavirus vaccine in its late-stage trial developed an allergic reaction, research has shown.
The much-anticipated jab is the first coronavirus vaccine to be approved in the UK, with thousands of vulnerable adults being immunised at hospital hubs on 8 December.
The UK’s vaccine regulator has warned, however, anyone with a “history of significant allergic reactions” should bypass the jab.
This precautionary guidance was issued after two NHS workers developed allergic reactions the day the vaccine was rolled out.
While it may sound alarming, just 0.63% of people who received the jab in Pfizer-BioNTech’s clinical trial endured the side effect, which did not stop the regulator granting approval.
This rate of allergic reactions was similar to those who received a placebo shot, at 0.51%.
Experts have 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.
The Medicines and Healthcare products Regulatory Agency (MHRA) – the UK’s vaccine regulator – has said anyone who has “significant reactions” to drugs, food or other jabs should avoid the coronavirus vaccine.
It is unclear how a significant reaction is defined.
The two unnamed NHS workers are said to have had an anaphylactoid reaction, which usually causes a mild rash, breathlessness and sometimes a decline in blood pressure.
This is much less serious than anaphylaxis, a potentially life-threatening response to an allergen.
Both of the workers, who have a history of serious allergies and carry adrenalin pens with them, recovered after treatment.
It is unclear what ingredients of the vaccine they reacted to.
Watch: Pfizer’s coronavirus vaccine is safe, says FDA
Off the back of the phase three trial, the FDA noted a “slight numerical imbalance of adverse events potentially representing allergic reactions, with more participants reporting hypersensitivity-related adverse events in the vaccine group”.
Among those who received the jab, 137 (0.63%) developed some form of allergic reaction, compared to 111 in the placebo group (0.51%). It is standard practice to exclude people with severe allergies from new drug or vaccine trials.
“As with all food and medications, there is a very small chance of an allergic reaction to any vaccine,” said Professor Peter Openshaw from Imperial College London.
“However, it is important we put this risk in perspective.
“Similar to the rollout of all new vaccines and medications, this new COVID-19 [the disease caused by the coronavirus] vaccine is being monitored closely by the MHRA.
“They will now investigate these [NHS worker] cases in more detail to understand if the allergic reactions were linked to the vaccine or were incidental.
“The fact that we know so soon about these two allergic reactions and the regulator has acted on this to issue precautionary advice shows this monitoring system is working well.”
Professor Stephen Evans from the London School of Hygiene & Tropical Medicine agreed the side effect is “not unexpected”.
“Allergic reaction occurs with quite a number of vaccines, and perhaps even more frequently with drugs,” he said.
“The only thing that is contraindicated with this vaccine (meaning you mustn’t have it) is hypersensitivity to the vaccine or any of the excipients (other things in the vaccine), but some people won’t know if they have hypersensitivity to some constituents of the vaccine.
“What would be wise, as the MHRA have already advised, would be for anyone who has known severe allergic reaction such that they need to carry an EpiPen, to delay having a vaccination until the reason for the allergic reaction has been clarified.
“For the general population this does not mean that they would need to be anxious about receiving the vaccination.
“One has to remember that even things like Marmite can cause unexpected severe allergic reactions.”
A Pfizer spokesperson added: “We have been advised by MHRA of two yellow card reports that may be associated with allergic reaction due to administration of the COVID-19 BNT162b2 vaccine.
“As a precautionary measure, the MHRA has issued temporary guidance to the NHS while it conducts an investigation in order to fully understand each case and its causes.
“Pfizer and BioNTech are supporting the MHRA in the investigation.
“In the pivotal phase three clinical trial, this vaccine was generally well tolerated with no serious safety concerns reported by the independent Data Monitoring Committee.
“The trial has enrolled over 44,000 participants to date, over 42,000 of whom have received a second vaccination.”
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