The British vaccination campaign against Covid-19 had barely begun when it hit its first snag.
On 9 December Two staff working for the British National Health Service (NHS) had an allergic reaction after they received the vaccine developed by Pfizer in collaboration with BioNTech. Both were treated quickly and were recovering well, authorities in the UK confirmed.
The UK Medicines and Healthcare products Regulatory Agency has since issued a precautionary warning, advising people not to get inoculated with the Pfizer vaccine if they have a history of acute allergic reactions.
An advisory panel of US experts said Thursday they would follow Britain’s lead with an allergy warning after recommending emergency approval there for the Pfizer vaccine.
A rare side effect
“This is appropriate advice,” Dr Louisa James, an immunology researcher at Queen Mary University in London, told FRANCE 24. “We now know that the two people concerned had a medical history and carried treatment to deal with strong allergic reactions.”
The two healthcare workers were carrying Anapen, an emergency treatment of adrenaline injected into the body in case of anaphylactic shock, which manifests as a severe allergic reaction.
According to Allergy UK, one in 1,000 people is at risk of anaphylactic shock after exposure to an allergen they have a sensitivity to. This type of allergic response “affects the cardiovascular, respiratory and gastrointestinal systems and causes severe skin rashes. The blood pressure can drop and breathing can become difficult,” Professor Saad Shakir, director of the Drug Safety Research Unit, a British health NGO, said in an interview with the Science Media Centre website.
In the case of the two NHS workers, however, neither had anaphylaxis, which is a more extreme reaction that can even be fatal. “It appears to be an anaphylactoid or pseudo-anaphylactic reaction, which leads to similar but less severe symptoms,” Professor Shakir explained.
Anaphylactoid reactions are linked to certain foods or medicines but also vaccines, including the annual flu jab.
“Cases of severe allergic reactions have been reported for all vaccines, but they remain rare,” Nilsson Lennart, a researcher at the Linköping Allergy Centre in Sweden and the author of a 2017 study on vaccines and allergies, told FRANCE 24. He added that cases of anaphylactic shock typically occur at a rate of 1.5 for every one million doses of vaccine administered.
Finding the cause
The pharmaceutical industry widely recognises the risk of allergic reaction and Pfizer knew it existed in the case of its Covid-19 vaccine.
“The data published by the laboratory indicate that about 0.6% of patients had some form of allergic reaction after administration of the dose during phase three clinical trials,” said Professor Stephen Evans, a pharmacoepidemiology researcher in the Department of Medical Statistics at the School of Hygiene and Tropical Medicine in London.
Pinpointing exactly what led to the allergic reaction may have its challenges as the Pfizer vaccine employs completely new technology, with no precedent for comparison. Yet investigations may lead to an additive commonly used in older vaccines.
“These kinds of side effects are known to be possibly linked to ingredients used to stabilise vaccines, such as polyethylene glycol [a gel used to thicken certain fluids in drugs or cosmetics],” Dr. James said.
Indeed, Pfizer had disclosed it used one of these ingredients when it publicly released data on its vaccine.
Scientists agree that what may appear as an initial mishap does not portend safety issues for the Pfizer vaccine, or the other contenders poised for rollout.
“One has to remember that even things like marmite [spread] can cause unexpected severe allergic reactions,” Professor Evans said.
Vaccine skepticism, nonetheless, remains a concern, and the scientific community will have to be vigilant and transparent in its messaging on efficacy and safety if it is to mitigate vaccine hesitancy. Publishing data by independent scientific and medical journals is one strategy.
In additional data released in the New England Journal of Medicine on Thursday, Pfizer and BioNTech said the vaccine was 95% effective in a randomised controlled trial of more than 43,000 people. The journal’s editors described the vaccine’s development as a “triumph” for science.
With independent monitoring processes in place to advise both the scientific community and the public, robust scrutiny of Covid-19 vaccine programs should be assured. And with it high levels of public confidence in these vaccines to protect against a disease that has caused the worst health crisis in a century.
This article has been translated from the original in French.
