Back in January 2021, I had a patient who had experienced a delayed edematous plaque (very large and painful) at the site of injection several days after she received her first dose of Moderna's mRNA-1273. It lasted 5 to 6 days and then resolved. She was concerned about the second shot. She was still willing to get it in the same non-dominant arm but wanted to make sure that it is okay to do so. I told her it would be okay but advised her to get the jab in the other arm.
First of all, neither local injection-site reactions nor delayed-type hypersensitivity reactions are contraindications to subsequent vaccination. As reported by Dr. Blumenthal and colleagues in NEJM today, in a sample of 12 patients with delayed large local reactions to mRNA-1273, half the patients did not have a recurrence of large local reactions, a quarter had recurrent reactions that were of a lower grade than the initial dose, and the remaining quarter had recurrent reactions similar to the initial dose. Skin biopsy revealed that these were in fact type IV delayed T-cell mediated hypersensitivity reactions. The symptoms lasted a median of 6 days (range 2 to 11 days).
What can help with these severe skin reactions? Ice packs, oral antihistamines, and topical glucocorticoids. For antihistamine, it is best to use second-generation H1-receptor antagonists like loratadine 10 mg PO daily, fexofenadine 180-360 mg PO daily or even twice a day, or cetirizine 10 mg (this one might cause drowsiness). You can also use first-generation H1-receptor antagonists like diphenhydramine 25-50 mg every 4 hours as needed (max 300 mg/day) if you want to cause drowsiness. H2-receptor antagonists might help in combination with H1-receptor antagonists, like famotidine 20 mg twice a day. Common topical corticosteroids include hydrocortisone 1%, clobetasol propionate 0.05%, or triamcinolone 0.1%.
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