Utility of skin testing in assessment of post-AZD1222 vaccine (AstraZeneca) allergic reactions: case series in Vietnam

Abstract

The coronavirus disease 2019 (COVID-19) pandemic is a global health emergency with more than 200 million cases and 4.5 million deaths. Vaccination is one of the main preventive measures to bring the current COVID-19 pandemic under control. Vaccines may cause adverse events; however, the majority of those adverse events are not allergic. Anaphylaxis induced by vaccines occurs approximately at a rate of 1.3:1,000,000 doses of vaccine. Recent data indicate that the incidence of COVID-19 vaccine-induced anaphylaxis is higher than that of all previous vaccines. The rates of anaphylaxis caused by the novel mRNA vaccine BNT162b2 (Pfizer-BioNTech, Mainz, Germany) and mRNA-1273 (Moderna, Cambridge, MA) are 4.7:1,000,000 doses and 2.8:1,000,000 doses, respectively. Early data estimates the anaphylaxis rate after AZD1222 vaccination is 7.4:1,000,000 doses. Vaccine allergy is mainly caused by excipients rather than an active ingredient of the vaccine. For mRNA COVID-19 vaccines, PEG 2000 (a component of BNT162b2 and mRNA-1273) and tromethamine (in mRNA-1273) are thought to be the allergenic components, while polysorbate 80, a derivative of polyethylene glycol (PEG), is proposed as the culprit antigen of the AZD1222 vaccine. However, it remains unclear whether PEG, tromethamine, or polysorbate 80 cause all of the allergic reactions to these vaccines. It is currently recommended for those at high-risk of allergic reactions, such as people with suspected or confirmed allergy to the first dose of COVID-19 vaccine to have a vaccine from a different vaccine group or to have a graded dose of the same vaccine administered. Use of skin testing for COVID-19 vaccines and their components such as PEG and polysorbate in high-risk groups has been reported to confirm the diagnosis of vaccine-induced allergic reactions. However, the sensitivity, specificity, and predictive value of skin testing have not been evaluated. In this case series, we examined the utility of skin testing in patients who had allergic reactions after the first dose of the AZD1222 vaccine. Ten patients with suspected allergic reactions post vaccination visited our clinics of allergy and clinical immunology at Vinmec International Hospital, Times City. Their history of allergy and clinical manifestations were examined carefully. Of those, 6 had symptoms within 4 hours, defined as immediate reactions and the remaining 4 showed nonimmediate allergic reactions with onset of symptoms 5 to 12 hours after vaccination. Testing with PEG, polysorbate, and COVID-19 vaccines including AZD1222, BNT162b2, and mRNA-1273 was performed prior to the administration of a second dose of a vaccine.