Israeli data identified reactions in 2% of high-risk Pfizer vaccine recipients

Allergic reactions to the BNT162b2 mRNA vaccine (Pfizer-BioNTech) were rare among highly allergic people enrolled in a prospective cohort study from Israel, with 98% having no such reactions.

Among the highly allergic patients—identified using an algorithm developed by the researchers—only 2% experienced an allergic reaction to either the first or second dose of the vaccine, and 0.7% (three total reactions) involved anaphylaxis.

The Israeli research is among the first to examine Covid-19 vaccination outcomes associated with an immunization strategy designed to address potential risks associated with vaccinating very high-risk people with a history of allergic disease.

“We created an algorithm for rapid screening of individuals who were potentially at risk of immediate allergic reaction to the BNT162b2 vaccine,” wrote researcher Ronen Shavit, MD, of Sheba Medical Center, Tel-Hashomer, Israel, and colleagues in JAMA Network Open. “This simple method can be easily implemented in any country and allowed 95% of applicants to be immunized in the regular settings in Israel.”

A nationwide roll out of the BNT162b2 vaccine began in Israel in December of 2020, and by early March of this year more than 4.8 million people in the country had received a first dose and more than 3.5 million had received two doses of the vaccine.

During a three-month period (late December 2020 to late March 2021), just over 8,100 patients with allergies who applied to the Covid-19 vaccine referral center at Sheba Medical Center underwent risk assessment using the allergic risk algorithm.

Patients considered at low risk of allergic reactions included those with a history of sensitivity to aeroallergens or insect bite, food, latex, or contrast media or prior non-anaphylactic reaction to a single drug group or those who had chronic urticaria.

Patients receiving immunotherapy or biologic therapy were instructed to delay that treatment for at least one week after immunization with the BNT162b2 vaccine. Patients at low risk of allergic reactions were recommended for immunization in regular settings, with 30 minutes of observation after immunization.

Patients who were not clearly at low risk of allergic reactions completed a questionnaire designed to further determine risk, and these people were also referred for further assessment at the clinical immunology and allergy department.

Patients were considered to be at high risk for allergic reactions if they had a prior anaphylactic reaction to any drug or vaccine, multiple drug allergies, multiple allergies, or mast cell disorders. Patients deferred by their GP or local allergist or the immunization team were also considered high risk.

This high-risk group were sent to a referral center to be immunized with 2 hours of observation by a dedicated allergy team after vaccination. Premedication was not recommended prior to receiving the first dose of the vaccine unless patients were regularly treated with these drugs (e.g., antihistamines). Patients with an allergy to PEG and/or two or more injectable drugs were rejected from vaccination, according to Israeli health recommendations at that time.

Of the 429 people who were deemed highly allergic based on the algorithm, 304 (70.9%) were women and the mean (SD) age was 52 (16) years.

After the first dose of the BNT162b2 vaccine, given under allergic specialist supervision, 420 patients (97.9%) had no immediate allergic event, 6 (1.4%) developed minor allergic responses, and 3 (0.7%) had anaphylactic reactions.

During the study period, 218 highly allergic patients (50.8%) received the second vaccine dose; 214 (98.2%) of these participants had no allergic reactions and 4 patients (1.8%) had minor allergic reactions.

Other immediate and late reactions were comparable to those seen in the general population, except for delayed itch and skin eruption, which were more common among allergic patients.

The researchers noted that vaccine-associated anaphylaxis is rare, with an estimated incidence of one reaction per 1 million injections for most widely given vaccines.

The anaphylaxis rate with the BNT162b2 vaccine was higher than this in early reports from the U.S. Centers for Disease Control and Prevention, with estimates of 4.7 to 11 anaphylaxis cases per 1 million doses reported. Four-out-of-five (81%) anaphylaxis reactions reported by the CDC occurred among people with a history of allergies or prior anaphylaxis events.

A more recent analysis of mRNA vaccine reactions from Mass General Hospital in Boston suggested an even higher anaphylaxis rate.

“In our highly allergic cohort, prior anaphylaxis was reported by 63% of patients,” the researchers wrote. “This finding suggests that, 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.

“Nonetheless, most patients in our cohort were safely immunized and all allergic and anaphylactic reactions were treated successfully at the immunization site with no requirement for hospitalization and/or further intervention.”

In accompanying commentary, Elizabeth J. Phillips, MD, of Vanderbilt University Medical Center, Nashville, wrote that important questions remain regarding Covid-19 vaccination risk among highly allergic people, including whether an allergic reaction to a first dose of mRNA vaccine is a contraindication to a second dose and what specific risk factors are associated with anaphylactic reactions to Covid-19 mRNA vaccines.

“Controlled studies of SARS-CoV-2 mRNA vaccines in observed populations with carefully timed samples will help define risk factors and mechanisms of allergic reactions, Phillips wrote. “This understanding will be critical to the optimization of mRNA vaccine technology and is paramount because mRNA vaccines are a facile and adaptable platform that can be used to target new SARS-CoV-2 variants and a wide variety of pathogens and disease processes.”

  1. Allergic reactions to the BNT162b2 mRNA vaccine were rare among highly allergic people enrolled in a prospective cohort study from Israel, with 98% having no such reactions.

  2. Among the highly allergic patients—identified using an algorithm developed by the researchers—2% experienced an allergic reaction to either the first or second dose of the BNT162b2 mRNA vaccine, and 0.7% (3 total reactions) involved anaphylaxis.

Salynn Boyles, Contributing Writer, BreakingMED™

Funding for this research was provided by the Sheba Fund for Health Services and Research. Researcher Gili Regev-Yochay reported receiving personal fees from Teva and grants from Pfizer outside the submitted work. No other researchers reported relevant disclosures.

Cat ID: 926

Topic ID: 79,926,933,926,99,927,928,934