Stanley Weiss started getting allergy shots at age 5. At about 8, he had a reaction to something — he doesn’t know what — that was so severe the family doctor had to rush to his house to give him a shot of epinephrine. Nuts gave him hives and made his tongue swell. A run through freshly cut grass in medical school gave him an asthma attack so bad that he could barely breathe. He’s had strong reactions to medications.

Now 66, he carries both a rescue inhaler and an EpiPen, a device that delivers epinephrine quickly during a severe allergic reaction known as anaphylaxis.

So it has been with great interest that Weiss, now an epidemiologist and professor at the Rutgers New Jersey Medical School, has followed news of rare but serious allergic reactions to Pfizer’s new COVID-19 vaccine.

Public health authorities in Great Britain have warned people with a history of anaphylactic attacks to hold off getting the shots. United States officials say the shots are mostly OK for this population in controlled settings where people can be observed for 30 minutes after getting the injection and treatment is available quickly. Those who have had bad reactions to specific COVID-19 vaccine ingredients are an exception and those who have had allergic responses to other vaccines should talk with their doctors, the U.S. Centers for Disease Control and Prevention (CDC) says.

Weiss, who is not providing direct patient care, is not in the high-priority group of health-care workers who are now being offered the vaccine. If he were, though, he’d get it.

“The risk of getting COVID-19 is very high right now, and the chance of becoming very ill is also very high, and you have to weigh the benefits with the risks,” he said. “The benefits are clear, and the risks are very low.”

A CDC official reported that there were six severe reactions — none lethal — among the first 272,000 people vaccinated for COVID-19 in the U.S., about 1 in 45,000. While one recipient in Alaska needed hospital care, others with serious reactions have responded to on-site treatment. For most vaccines, doctors expect 1 serious allergic reaction per million people vaccinated, said Lawrence Livornese, an infectious-diseases doctor who is chair of medicine at Main Line Health.

Several area hospitals that have begun vaccinating employees said no one has had a severe reaction.

Pablo Tebas, a vaccine researcher and a professor of infectious diseases at the Perelman School of Medicine at the University of Pennsylvania, said math makes the decision to get the vaccine easy. While allergic reactions to the shots are very unusual, COVID-19 has killed 2.7% of people with known cases in Philadelphia. COVID-19 patients are dying every day in Penn’s ICUs, he said. “The risk of [getting the vaccine] in a controlled environment is much less, orders of magnitude less, than getting COVID,” he said.

The big problem is that no one knows which vaccine ingredient could be triggering these responses. Plus, you probably wouldn’t know if you’re allergic to these things anyway. Here’s what the FDA says is in Pfizer’s vaccine: “mRNA, lipids ((4-hydroxybutyl)azanediyl)bis(hexane-6,1-diyl)bis(2-hexyldecanoate), 2 [(polyethylene glycol)-2000]-N,N-ditetradecylacetamide, 1,2-Distearoyl-sn-glycero-3- phosphocholine, and cholesterol), potassium chloride, monobasic potassium phosphate, sodium chloride, dibasic sodium phosphate dihydrate, and sucrose.”

Well, OK then. With a couple exceptions, those are not household names. “There’s nothing in that list that made my ears perk up as to what would be definitively the culprit,” said Weiss, who is a member of the New Jersey Allergy, Asthma and Immunology Society.

The National Institutes of Health said this week that it is planning a clinical trial to sort this out.

People with a history of anaphylaxis were not included in the trials for either the vaccine developed by Pfizer and partner BioNTech or one created by Moderna, which received emergency authorization last week. Severe reactions were not reported during those trials, but surfaced after the Pfizer vaccine was given to the general public. The Moderna vaccine is just now getting broader use.

Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said last week that polyethylene glycol (PEG), which is in both vaccines, is an ingredient that’s under suspicion. It is found in many drugs, toothpastes, and cosmetics and has been known to cause rare, anaphylactic reactions.

Weiss thinks it’s premature to assume PEG is the problem. Typically, he said, it’s “not terribly chemically reactive.”

The good news, he said, is that the bad reactions are highly unusual. “What it is that’s causing people to react is not clear, but it’s rare,” he said. It’s also “reassuring,” he said, that the government is monitoring reactions and reporting them quickly.

This is Stanley Weiss's EpiPen.
Courtesy of Stanley Weiss.
This is Stanley Weiss's EpiPen.

Livornese thinks it is reasonable to focus on PEG as the vaccine ingredient most likely to cause problems. Most of the other ingredients are benign, he said. Some people may know they’re allergic to PEG.

Weiss said the most common triggers of extreme allergic reactions are bee stings, nuts and peanuts. People can be allergic to many foods.

The CDC says people with these sorts of allergies, along with those who have reacted to latex, pets or oral medications can safely get the vaccines. It says if you have a severe reaction to the first dose of a vaccine, you shouldn’t get the second.

Livornese said people who have had severe allergic reactions to anything should tell their vaccinator and expect a 30-minute observation period. “People with allergies to one thing tend to have a higher risk of allergies to other things,” he said. Even so, he thinks that people with allergies to food, medications and environmental factors should go ahead and get the vaccine. People who have reacted to other injectable agents should talk to their doctors first.

Livornese, who has gotten the first dose of vaccine himself, is a strong proponent of the shot. “This is an important strategy to help stop this pandemic,” he said.