Only a small fraction of those who have received a coronavirus vaccine have experienced serious allergic reactions. But media reports of those reactions have made some people nervous about getting the shots.
Doctors at UT Southwestern Medical Center are co-leading a national, federally funded study to examine the frequency of allergic reactions to the Pfizer and Moderna vaccines among those with a history of severe allergies. They hope that additional data will alleviate people’s fears about getting inoculated.
“If we can help get the message out that this vaccine is safe, even in people that might be at high risk, this may help with vaccine hesitancy across the board,” said Dr. Rebecca Gruchalla, director of the division of allergy and immunology at UT Southwestern. She co-designed the study and is one of its three lead investigators.
Estimates of the share of Pfizer and Moderna vaccinations that have triggered severe allergic reactions range from about .00025% to .025% of doses, according to studies.
In a report published last month in the Journal of the American Medical Association, 16 of 64,900 employees of a major hospital system who received either the Pfizer or Moderna vaccine developed a severe allergic reaction called anaphylaxis, or .025% of participants.
A larger share, about 2% of those who received the vaccine, suffered milder allergic reactions such as itching. Of those who suffered any allergic reaction, about 63% had a history of allergies. All individuals recovered after treatment.
No known deaths have resulted from allergic reactions to the shots, Gruchalla said.
Anaphylaxis is an immediate reaction that occurs in one or more parts of the body beyond the injection site, according to the National Institutes of Health. The reaction can be life-threatening and is often treated with an injection of the hormone epinephrine. Those prone to severe allergic reactions carry with them epinephrine auto-injectors such as EpiPens.
The JAMA study pointed out that, based on national allergy rates, almost 4,000 of the 64,900 employees who were vaccinated likely had histories of severe food or medication allergies yet received the shots safely.
The new study will enroll 3,400 adults ages 18 to 69 years at up to 35 sites nationwide, including at UT Southwestern. About 60% of study participants will have either a history of severe allergic reactions to food, bee stings or drugs, or a diagnosis of a mast cell disorder, a disease that predisposes a person to life-threatening reactions similar to allergies. The other 40% of participants will have no history of allergies.
The goal of the trial is to determine whether people who are highly allergic or have a mast cell disorder are at increased risk for an immediate, severe allergic reaction to the Moderna or Pfizer vaccines. If such an allergic reaction occurs during the study, investigators will examine the biological mechanism behind the reactions and whether a genetic pattern or other factors can predict who is at most risk.
“The goal is to prove that the vaccines are safe, including in individuals who have histories of underlying allergies,” said Dr. David Khan, an allergist at UT Southwestern who is leading the trial at the Dallas hospital system.
The results are important not only for the current Pfizer and Moderna vaccines but for future vaccines that use similar platforms, said Gruchalla.
The trial will likely expand to individuals ages 12 and up within the next few weeks, now that the U.S. Food and Drug Administration has authorized the use of the Pfizer vaccine in young adolescents, said Khan.
Another focus of the study is to help assess which vaccine components may trigger allergies. Early on, investigators focused on the additive polyethylene glycol, which is present in both the Pfizer and Moderna vaccines and better known as the main ingredient in the over-the-counter laxative Miralax.
“The evidence to date suggests that that’s probably not the main cause of people who’ve had reactions to the vaccine,” said Khan. “At this point, we still don’t know, but it’s one of the things that we’re attempting to look at with the study.”
Current FDA guidance says people with known allergies to polyethylene glycol or to other vaccine ingredients should not receive the Pfizer or Moderna shots.
Khan added that the risks of severe allergic reactions from the vaccines, even for those with a history of allergies, is low. But patients in that category should come to their appointments prepared to treat any possible reactions.
Those who still feel nervous should consider enrolling in the study, said Khan.
“People who’ve suffered from severe allergic reactions in the past may be hesitant about getting the vaccine in the pharmacy or a vaccine center,” he said. “One thing we hope to provide with our study is a safe environment.”
Those who enroll in the trial, which is sponsored and funded by the National Institutes of Health, will be assigned at random to receive either the Pfizer vaccine, the Moderna vaccine or a placebo followed by the Pfizer or Moderna vaccine. All participants ultimately will receive a full two-dose course of either vaccine under close medical supervision.
Results are expected in late summer 2021.
Those interested in enrolling in the trial should call 214-799-0751 or email sarsvaccine@utsouthwestern.edu
Friday May 14, 5:15 pm: Updated to reflect a new email address for the clinical trial.
