Caution against injudicious vaccine allergy skin tests: Adverse reactions after intradermal COVID-19 vaccine testing.

The coronavirus disease 2019 (COVID‐19) vaccination program in Hong Kong has two vaccines available: the Pfizer‐BioNTech Comirnaty (BNT) and the Sinovac Coronavac (SV) vaccines. All individuals with suspected allergic reaction to the first dose vaccine should be referred to an allergist for a workup, which may include vaccine skin testing. However, selecting individuals for testing should be based on clinical suspicion as to avoid false‐positive/false‐negative results or adverse reactions. To demonstrate, we report a case of severe delayed “positive” reaction following an intradermal test (IDT) for workup of a suspected immediate‐type allergy to SV.

CASE REPORT

A 48‐year‐old woman, with no history of drug allergy, was referred to our VAS Clinic for suspected SV allergy. She developed generalized urticaria around 1 hour after vaccination. There was no extracutaneous involvement and no features of anaphylaxis. Her urticaria persisted for a few days until spontaneous resolution. In view of a possible immediate‐type allergy to SV, skin prick tests and IDT to SV and BNT (both fresh and undiluted, as per departmental protocol) were performed on her right forearm, and they were all unequivocally negative upon immediate readings. The patient also did not develop any immediate‐type symptoms following skin testing. It was recommended that she proceed with her second dose of SV. In view of prior sensitization, she was warned of possible delayed reactions at her skin test sites and was prescribed topical mometasone furoate 0.1% ointment.

The patient complained of progressive erythema and swelling over both prior SV and BNT IDT sites, which developed into blistering lesions over the next few days despite good adherence to topical steroid (Figure 1). This was accompanied by severe tenderness and underlying edema. She was prescribed a 3‐day course of oral steroids, and her symptoms gradually resolved with some residual hyperpigmentation. Two weeks later, she tolerated her second dose of SV uneventfully.

FIGURE 1

Delayed “positive” reactions with Sinovac Coronavac (SV) and Pfizer‐BioNTech Comirnaty (BNT) vaccine intradermal sites of index patient

DISCUSSION

Although the optimal workup for suspected COVID‐19 vaccine–associated allergic reactions remains unclear, skin testing with vaccines or excipients have been advocated with mixed results. Reminiscent of the Mantoux test for diagnosis of latent tuberculosis, delayed reactions at the COVID‐19 vaccine IDT sites are expected and have been consistently seen in all patients following first‐dose vaccination, indicating prior sensitization rather than clinical allergy. Reactions at both BNT and SV IDT sites invariably occur regardless of which type of COVID‐19 vaccine was administered prior. Likely due to its greater immunogenicity, BNT IDT reactions are often more pronounced than SV reactions (Figure 2). It is important to note that these delayed “positive” IDT do not seem to correlate with subsequent vaccine reactions. We strongly caution against the injudicious use of vaccine skin testing in the assessment of suspected vaccine‐associated allergies.

FIGURE 2

Milder delayed reactions of two other patients with Sinovac Coronavac (SV) and Pfizer‐BioNTech Comirnaty (BNT) vaccines (day 2 after intradermal testing). All patients completed the second dose of vaccination without complications

CONFLICT OF INTEREST

All authors declare no conflicts of interest.

AUTHOR CONTRIBUTIONS

Valerie Chiang: Conceptualization (lead); investigation (lead). Pearl Mong: Data curation (equal); investigation (equal); writing – original draft (lead). Edward Chan: Investigation (equal); methodology (equal); writing – original draft (equal); writing – review and editing (equal). Elaine Au: Writing – review and editing (equal). Philip Li: Conceptualization (equal); data curation (equal); investigation (equal); resources (equal); supervision (equal); writing – review and editing (lead).