Potential Pfizer COVID Vaccine Allergic Reactions Should Not Make Public 'Anxious'

Reports that two people suffered allergic reactions after taking the Pfizer/BioNTech in the U.K. should not make the general public "anxious," experts have said.

U.K. regulators said on Wednesday that people with "significant" allergies should not currently receive the Pfizer/BioNTech vaccine.

The announcement came after two members of the country's National Health Service (NHS) who were vaccinated on Tuesday experienced allergic reactions afterward, Professor Stephen Powis, national medical director for the NHS in England, said in a statement.

Both individuals have a history of "significant" allergic reactions severe enough that they carry an adrenaline autoinjector with them at all times. The pair developed "anaphylactoid reaction" symptoms and are "recovering well" after receiving treatment, Powis said.

Regulators have not yet confirmed that the adverse reactions were caused by the vaccine, and if they were, what ingredient in the vaccine was responsible.

The U.K.'s Medicines and Healthcare products Regulatory Agency (MHRA) issued precautionary advice to NHS trusts administering the shot that anyone "with a history of a significant allergic reaction to a vaccine, medicine or food should not receive the Pfizer/BioNtech vaccine," for now.

"Resuscitation facilities should be available at all times for all vaccinations. Vaccination should only be carried out in facilities where resuscitation measures are available," the advice stated.

From Wednesday, anyone set to receive the Pfizer/BioNTech vaccine in the U.K. will be asked about their history of allergic reactions.

"As is common with new vaccines the MHRA have advised on a precautionary basis that people with a significant history of allergic reactions do not receive this vaccination after two people with a history of significant allergic reactions responded adversely yesterday," Powis said on Wednesday.

Earlier in December, the U.K. became the first country in the world to approve the Pfizer/BioNTech shot, with the vaccination program beginning this week. Workers in care homes, hospital patients and NHS staff are first in line to receive the vaccine.

"Allergic reaction occurs with quite a number of vaccines, and perhaps even more frequently with drugs. So it is not unexpected," Stephen Evans, a professor of pharmacoepidemiology at the London School of Hygiene & Tropical Medicine, said in a statement.

A study of the data from the large-scale, Phase III clinical trial evaluating the Pfizer/BioNTech vaccine—published yesterday—showed that around 0.6 percent of people who received the shot had some form of allergic reaction during the testing, compared to about 0.5 percent in the group that were given a placebo.

"So there was a genuine excess of allergic reaction but this was small and the true rate is not known, and there is a lot of uncertainty around that estimate," Evans 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."

The MHRA will now conduct an investigation to fully understand the allergic reactions experienced by the two NHS workers and their causes.

"Similar to the rollout of all new vaccines and medications, this new COVID-19 vaccine is being monitored closely by the MHRA. They will now investigate these cases in more detail to understand if the allergic reactions were linked to the vaccine or were incidental," Professor Peter Openshaw, a professor of experimental medicine at Imperial College London, said in a statement.

"The fact that we know so soon about these two allergic reactions and that the regulator has acted on this to issue precautionary advice shows that this monitoring system is working well."

A spokesperson for American pharmaceutical giant Pfizer said the company and its German partner BioNtech were supporting the MHRA investigation, noting that the clinical trials assessing the vaccine had demonstrated no serious safety concerns.

"In the pivotal Phase III 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."

Openshaw said there is a "very small chance" of an allergic reaction to any vaccine but it is "important that we put this risk in perspective."

Pfizer's clinical trial protocols for the vaccine stated that individuals with a "history of severe adverse reaction associated with a vaccine and/or severe allergic reaction (for example, anaphylaxis) to any component of the study interventions," were excluded from taking part.

The MHRA had previously published guidance for prescribing the vaccine in the U.K., stating that the shot should not be administered to people who are allergic to the active substance or any other ingredients it contains.

But the regulator did not advise people with a history of severe allergic reactions in general to avoid the vaccine before its rollout this week.

Several vaccines currently on the market carry health warnings for people who are susceptible to allergic reactions.

Individuals like the two NHS workers who need to carry EpiPens are at an increased risk of an allergic reaction from vaccines compared to the general population without a history of severe allergy, Dr. Penny Ward, a professor of pharmaceutical medicine at King's College London, said in a statement.

"Previous epidemiological studies of anaphylaxis suggests that an anaphylactic reaction might be observed within a community in up to 30 out of 100,000 people followed over a year, by chance alone," she said.

"As these two events occurred in people with a history of severe allergy, it is sensible of the MHRA to draw attention to these reports and to suggest that individuals with a history of severe allergy not receive the vaccine at this time."

Nurse administers Pfizer/BioNTech COVID-19 vaccine
A staff nurse at the Royal Cornwall Hospital prepares to administer the Pfizer/BioNTech COVID-19 vaccine as the hospital began their vaccination programme on December 9, 2020 in Truro, United Kingdom. Hugh Hastings/Getty Images