Pfizer Vax Safe, Even Among the Highly Allergic

Most highly allergic adults were able to safely receive the two-dose series of the Pfizer/BioNTech COVID-19 vaccine (BNT162b2; Comirnaty), a prospective single-center study found.

Of 429 highly allergic patients who received the first dose of the mRNA vaccine, mild allergic reactions occurred in 1.4% and 0.7% experienced anaphylaxis, reported Nancy Agmon-Levin, MD, of Sheba Medical Center in Ramat-Gan, Israel, and colleagues.

After 218 of the highly allergic patients received the second dose, 1.8% experienced minor allergic reactions and none had anaphylaxis, the authors wrote in JAMA Network Open.

The study “provides additional reassurance that most highly allergic persons will not have allergic reactions to the SARS-CoV-2 mRNA vaccines,” said Elizabeth Phillips, MD, of Vanderbilt University in Nashville, in an accompanying editorial.

CDC’s current interim recommendations state that the COVID-19 vaccine is contraindicated in individuals with a prior severe allergic reaction (such as anaphylaxis) after the first dose, as well as in patients with a history of immediate allergic reaction to any component of the vaccine. Recent research, however, has suggested that second doses can be administered safely, even among those with severe allergic reactions to the first dose.

Agmon-Levin and colleagues noted that polyethylene glycol (PEG) is thought to be responsible for allergic reactions to Pfizer’s vaccine. Prior research has demonstrated an anaphylaxis rate of 4.7 cases per million doses with the mRNA vaccine, with most cases occurring among women (90%) and those with prior allergies (81%).

“Although the precise risk factors for allergic reactions to the BNT162b2 vaccine are yet to be revealed, prior high-risk allergies may enable screening of patients at risk for allergic response to this vaccine,” the authors wrote.

The researchers created an algorithm for screening individuals at risk of immediate allergic reaction to vaccination. Those with allergies who applied for vaccination were referred for assessment by a clinical team and completed a questionnaire. Patients deemed to be at the highest risk of allergic reaction received the vaccine in a separate referral center, with an extended observation period of 2 hours by “a dedicated allergy team.” Lower risk patients were vaccinated in a regular setting.

High-risk patients were defined as individuals with a history of severe allergic reactions, multiple allergies, multiple drug allergies, or mast cell disorders. Low-risk patients had minor allergies (latex, insects, or food). Patients with PEG allergies or multiple injectable drug allergies were excluded.

From December 2020 to February 2021, there were 8,102 patients with allergies who applied to the vaccine referral center. Second doses were administered 21 days after the first. Early adverse events were defined as occurring within 2 hours of vaccination, and resolving within 24 hours.

Overall, 6,883 patients were recommended to receive the vaccine in standard settings, while 1,219 patients (15%) were referred. Of these, 785 patients were defined as low-risk and received vaccination in regular settings. The authors noted no reports of severe allergic reactions among this population. Five patients were ineligible to be vaccinated.

The remaining 429 high-risk patients had a median age of 52, and 71% were female. There were 63% who had prior anaphylaxis, 32% with multiple drug allergies, and 30% with multiple allergies.

Most of the high-risk patients had no immediate adverse events after the first dose (96%; 412 patients). Ten patients had nonallergic reactions.

Among nine patients with early allergic reactions, anaphylactic reactions such as bronchospasm, skin eruption, itching and shortness of breath, occurred in three patients. These were treated by adrenaline, antihistamines, and an inhaled bronchodilator; one patient received systemic glucocorticoids. None of these patients were hospitalized, and symptoms resolved within 2 to 6 hours, the authors said. None of these patients went on to receive a second dose.

The other six had mild immediate allergic reactions; none of the nine patients reported recurrent or ongoing allergic symptoms at 2 weeks follow-up, the authors noted.

After the second dose, four patients had minor allergic reactions including flushing and cough. Three of the patients also had mild reactions after the first dose, the authors noted.

“Most high-risk patients who did not experience any adverse events from the first dose also did not exhibit a reaction to the second dose,” the authors said. “This finding may suggest that a shortened observation period may be sufficient after the second dose of the vaccine for patients who did not experience a reaction to the first dose.”

Limitations of the study included that the patients who were immunized in a regular setting were not actively followed up, as well as the use of self-reported questionnaires and medical records to determine history of allergic reactions.