Anaphylaxis after COVID mRNA vaccination relatively rare

Anaphylactic reactions warranting treatment after receipt of COVID-19 mRNA vaccinations appear to be relatively rare, according to a US study presented at AAAAI 2022.

Using the Kaiser Permanente Southern California (KPSC) database, the researchers identified 391,022 enrolled individuals (average age 64 years, 59.18 percent female) who had received COVID mRNA vaccinations between December 15, 2020 and November 3, 2021 at a KPSC centre and had ≥1 drug allergy. They then identified individuals who had received treatment for an acute-onset hypersensitivity event within 6 hours of vaccination.

A total of 606,273 COVID mRNA vaccinations were administered, 267,209 and 339,064 Pfizer BioNTech and Moderna, respectively. Of these, 372,745 were first doses (Pfizer BioNTech: 162,508; Moderna: 210,237). Treatment for hypersensitivity reactions was required in 0.027 percent of recipients (n=104; Pfizer BioNTech [n=36]; Moderna [n=68]; average age 53 years with two drug allergies, 86 percent female). [AAAAI 2022, abstract 168]

A total of 233,528 second doses were administered (Pfizer BioNTech: 104,701; Moderna: 128,827). Thirty-two individuals (0.0137 percent) required treatment for hypersensitivity events (Pfizer BioNTech [n=11]; Moderna [n=21]; average age 57 years with two drug allergies, 94 percent female).

Thirty-one reactions (26 following first dose) were treated with epinephrine, 119 (90 after first dose) were treated with antihistamines, and 40 (31 after first dose) treated with corticosteroids.

Only two of the reactions were later confirmed as anaphylactic reactions, corresponding to 3.3 per 1,000,000 doses administered. Of the 104 individuals who were treated for reactions after the first dose of the vaccine, 28 percent (n=29) received a subsequent dose of the vaccine, among whom only six (21 percent) required retreatment.

“COVID-19 mRNA vaccine-associated acute-onset hypersensitivity reactions are widely reported, but population-based incidence data on treated reactions and tolerance of subsequent doses is lacking,” the authors from Kaiser Permanente pointed out.

In this study, acute-onset hypersensitivity reactions warranting treatment were more common following the first dose of the vaccine, primarily in females with >2 drug allergies, and recipients of the Moderna vaccine, they continued.

Due to the lack of evident booster effect, the researchers suggested that most of the treated reactions were unlikely to be immunologically mediated. The low number of reactions after the second vaccine dose also suggest that “direct nanoparticle-induced complement activation” may be an unlikely mechanism.

Post-vaccine urticaria, angioedema rare

Another study, this time conducted using data from the COVID-19 Vaccine Allergy Case Registry of the Massachusetts General Hospital, Boston, Massachusetts, US, noted low rates of urticaria and/or angioedema in mRNA vaccine recipients. [AAAAI 2021, abstract L05]

The study included 455 individuals, of whom 13 percent (n=58; mean age 49 years, 84 percent female, 76 percent White) experienced urticaria and/or angioedema after COVID-19 vaccination.

Seventy-four percent of the documented urticaria and/or angioedema events occurred after the first vaccine dose, with no difference according to vaccine (50 percent each in Pfizer BioNTech and Moderna recipients). Forty-seven percent of events occurred >24 hours following vaccination, while 35 percent occurred at ≤4 hours and 19 percent >4 hours but ≤24 hours post-vaccine.

Ten individuals (17 percent) had a prior history of chronic urticaria and/or angioedema, while 23 (40 percent) had a history of other atopic comorbidities.

Sixty-seven percent of individuals were treated with antihistamines, 31 percent with oral corticosteroids, and 5 percent with epinephrine. Just 3 percent required hospitalization.

“Evidence-based information about side effects combats vaccine hesitancy,” highlighted the researchers.

“[In this study,] urticaria and/or angioedema events comprised 13 percent of clinician-reported COVID-19 vaccine allergy cases following mRNA vaccinations … the majority of cases occurred in those without underlying chronic urticaria and/or angioedema [and] most cases had onset after 4 hours and were mild,” they summarized.

“Given timing of onset and benign course, many urticaria and/or angioedema events after COVID-19 vaccination should not contraindicate future doses,” they concluded.