The decision by British drug regulators to recommend against use of the coronavirus vaccine made by Pfizer and BioNTech in people who have a history of severe allergic reactions has raised a number of concerns.
The regulators issued the warning after two health care workers, both with such a history, had a serious reaction, anaphylaxis, after receiving the vaccine on the first day it became available in Britain. Anaphylaxis can be life-threatening, with impaired breathing and drops in blood pressure that usually occur within minutes or even seconds after exposure to a food or medicine, or even a substance like latex to which the person is allergic.
Both workers were treated and have recovered, the regulators said.
British authorities have since clarified their concerns, changing the wording from “severe allergic reactions” to specify that the vaccine should not be given to anyone who has ever had an anaphylactic reaction to a food, medicine or vaccine. That type of reaction to a vaccine is “very rare,” they said.
Their update also said that a third patient had a “possible allergic reaction,” but did not describe it.
Officials of the U.S. Food and Drug Administration said on Thursday that because of the British cases they would require Pfizer to increase its monitoring for anaphylaxis and submit data on it once the vaccine comes into use. A panel of expert advisers to the F.D.A. voted on Thursday to recommend authorizing the vaccine for emergency use, but also expressed concerns about the need to track anaphylaxis. The agency usually accepts the experts’ recommendations, and the authorization is expected within days. Vaccinations could start next week in the United States.
The initial report on the British cases touched off alarm and confusion by advising that people who had ever had a “severe allergic reaction” to a food, drug or vaccine should not receive the vaccine. The nature of the reaction was not explained at first, leaving many people with allergies to food or bee stings wondering if the new vaccine would be safe for them.
But the regulators’ subsequent clarification specified that their advice applied to people who had ever gone into anaphylaxis. It urged people with a “history of serious allergies” to discuss it with their doctors “prior to getting the jab.”
The authorities also said the shots should be given only in settings equipped to resuscitate patients if needed, by giving injections of epinephrine, also known as adrenaline.
The two health care workers in Britain had experienced anaphylaxis in the past because of food allergies, a Pfizer official said during the F.D.A. meeting on Thursday. Both carried EpiPen-type devices to inject themselves with epinephrine in case of such a reaction.
They needed epinephrine to treat their reactions to the vaccine, and both recovered.
British health authorities said they would continue to investigate. It is not known whether an ingredient in the vaccine caused the workers’ reactions.
People with a history of an anaphylactic reaction to any vaccine were excluded from Pfizer’s studies, company officials said at the meeting on Thursday.
Among those who participated in the Pfizer trials, a very small number of people had allergic reactions. A document published by the F.D.A. on Tuesday said that 0.63 percent of participants who received the vaccine reported potential allergic reactions, compared to 0.51 percent of people who received a placebo.
In Pfizer’s late-stage clinical trial, one of the 18,801 participants who received the vaccine had an anaphylactic reaction, according to safety data published by the F.D.A. on Tuesday. None in the placebo group did.
Dr. Anthony Fauci, the nation’s leading expert on infectious diseases, said on Wednesday that the allergic reactions were concerning but most likely rare, the kind of effects that show up when a vaccine moves out of testing and into broader distribution.
“If I were a person that had an underlying allergic tendency, I might want to be prepared that I might get a reaction, and therefore be ready to treat it,” Dr. Fauci said, in a webcast moderated by Dr. Sanjay Gupta of CNN, sponsored by Harvard and The New England Journal of Medicine.
Dr. Fauci acknowledged that the problem could turn out to affect a lot of people.
“That’s one of the reasons why it’s important to cover the waterfront with different vaccine platforms,” he said, adding, “If in fact we do find out that there is a consistent issue of a certain subset of people like those with allergic reactions, you’ll always have other vaccine platforms that you can use and hopefully you will not see that with those other platforms.”
Dr. Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia, said the initial, broad recommendation in Britain mentioning severe allergic reactions seemed to be an overreaction that could needlessly scare many people away from a desperately needed vaccine in the middle of a raging pandemic.
Millions of people in the United States are allergic to foods like eggs or peanuts, as well as medicines or bee stings, and have had reactions that were serious enough to lead doctors to advise them to carry epinephrine injectors. But that does not necessarily mean the vaccine is risky for them, he said. About five percent of children and four percent of adults in the United States have food allergies, according to the National Institute of Allergy and Infectious Diseases.
Fewer than one in a million recipients of other vaccines a year in the United States have an anaphylactic reaction, Dr. Offit said.
Those reactions are treatable, and much easier to control than a severe case of Covid-19, he said.
Many people with allergies to foods, bee stings or medicines have received multiple vaccines without problems.
As the coronavirus vaccine get closer to U.S. authorization, here are some questions you may be wondering about:
- If I live in the U.S., when can I get the vaccine? While the exact order of vaccine recipients may vary by state, most will likely put medical workers and residents of long-term care facilities first. If you want to understand how this decision is getting made, this article will help.
- When can I return to normal life after being vaccinated? Life will return to normal only when society as a whole gains enough protection against the coronavirus. Once countries authorize a vaccine, they’ll only be able to vaccinate a few percent of their citizens at most in the first couple months. The unvaccinated majority will still remain vulnerable to getting infected. A growing number of coronavirus vaccines are showing robust protection against becoming sick. But it’s also possible for people to spread the virus without even knowing they’re infected because they experience only mild symptoms or none at all. Scientists don’t yet know if the vaccines also block the transmission of the coronavirus. So for the time being, even vaccinated people will need to wear masks, avoid indoor crowds, and so on. Once enough people get vaccinated, it will become very difficult for the coronavirus to find vulnerable people to infect. Depending on how quickly we as a society achieve that goal, life might start approaching something like normal by the fall 2021.
- If I’ve been vaccinated, do I still need to wear a mask? Yes, but not forever. The two vaccines that will potentially get authorized this month clearly protect people from getting sick with Covid-19. But the clinical trials that delivered these results were not designed to determine whether vaccinated people could still spread the coronavirus without developing symptoms. That remains a possibility. We know that people who are naturally infected by the coronavirus can spread it while they’re not experiencing any cough or other symptoms. Researchers will be intensely studying this question as the vaccines roll out. In the meantime, even vaccinated people will need to think of themselves as possible spreaders.
- Will it hurt? What are the side effects? The Pfizer and BioNTech vaccine is delivered as a shot in the arm, like other typical vaccines. The injection won’t be any different from ones you’ve gotten before. Tens of thousands of people have already received the vaccines, and none of them have reported any serious health problems. But some of them have felt short-lived discomfort, including aches and flu-like symptoms that typically last a day. It’s possible that people may need to plan to take a day off work or school after the second shot. While these experiences aren’t pleasant, they are a good sign: they are the result of your own immune system encountering the vaccine and mounting a potent response that will provide long-lasting immunity.
- Will mRNA vaccines change my genes? No. The vaccines from Moderna and Pfizer use a genetic molecule to prime the immune system. That molecule, known as mRNA, is eventually destroyed by the body. The mRNA is packaged in an oily bubble that can fuse to a cell, allowing the molecule to slip in. The cell uses the mRNA to make proteins from the coronavirus, which can stimulate the immune system. At any moment, each of our cells may contain hundreds of thousands of mRNA molecules, which they produce in order to make proteins of their own. Once those proteins are made, our cells then shred the mRNA with special enzymes. The mRNA molecules our cells make can only survive a matter of minutes. The mRNA in vaccines is engineered to withstand the cell's enzymes a bit longer, so that the cells can make extra virus proteins and prompt a stronger immune response. But the mRNA can only last for a few days at most before they are destroyed.
As a member of the F.D.A. advisory panel that met on Thursday, Dr. Offit voted in favor of authorizing the Pfizer vaccine. But during the panel’s discussion of allergic reactions, he said, “this issue is not going to die until we have better data.”
He said research should be done to find out whether an ingredient in the vaccine can cause allergic reactions, and whether people with other allergies might be especially sensitive to it.
Dr. Moncef Slaoui, the head of the government’s Operation Warp Speed program to develop vaccines, said on Wednesday that he thought U.S. experts would also advise people who have had severe allergic reactions to avoid the vaccine until the cases in Britain were fully explained.
Dr. William Schaffner, an infectious disease and vaccine expert at Vanderbilt University, said, “I wish Dr. Slaoui hadn’t gotten ahead of his skis.”
He said recommendations about who should or should not get the vaccine would be made by expert advisory panels to the Centers for Disease Control and Prevention, which will be meeting on Friday and this weekend.
Dr. Schaffner said it seemed unlikely that the main ingredient in Pfizer’s vaccine, genetic material called mRNA, would cause an allergic reaction.
Next week, the F.D.A.’s advisory panel will vote on whether to recommend authorizing a second coronavirus vaccine that uses mRNA, made by Moderna. The Moderna and Pfizer vaccines are similar but not identical: They use different types of fat particles, for instance, to coat the mRNA.
Dr. Schaffner said he knew of no evidence that people with food allergies were more likely than anyone else to have a severe reaction to a vaccine.
“We’ve dealt with allergies to all kinds of medicines and vaccines in medical practice, and we can do that in this circumstance also,” Dr. Schaffner said. “Everybody needs to be trained to be able to deal with this and deal with it promptly. I think we can manage this.”