To the Editor:
The Moderna COVID-19 messenger RNA (mRNA) vaccine was authorized for use on December 18, 2020, with the second dose beginning on January 15, 2021.1-3 Some individuals who received the Moderna vaccine experienced an intense rash known as “COVID arm,” a harmless but bothersome adverse effect that typically appears within a week and is a localized and transient immunogenic response.4 COVID arm differs from most vaccine adverse effects. The rash emerges not immediately but 5 to 9 days after the initial dose—on average, 1 week later. Apart from being itchy, the rash does not appear to be harmful and is not a reason to hesitate getting vaccinated.
Dermatologists and allergists have been studying this adverse effect, which has been formally termed delayed cutaneous hypersensitivity. Of potential clinical consequence is that the efficacy of the mRNA COVID-19 vaccine may be harmed if postvaccination dermal reactions necessitate systemic corticosteroid therapy. Because this vaccine stimulates an immune response as viral RNA integrates in cells secondary to production of the spike protein of the virus, the skin may be affected secondarily and manifestations of any underlying disease may be aggravated.5 We report a patient who developed a psoriasiform dermatitis after the first dose of the Moderna vaccine.
FIGURE 1. A, Scattered 2- to 5-mm, pink-erythematous, scaly plaques were present on the posterior trunk (back). B, Scattered scaly papules with mild macular erythema were present on the left upper chest and clavicular region, with pink to deep red–erythematous papules coalescing linearly on the neck and left shoulder 2 days after vaccination.
A 65-year-old woman presented to her primary care physician because of the severity of psoriasiform dermatitis that developed 5 days after she received the first dose of the Moderna COVID-19 mRNA vaccine. The patient had a medical history of Sjögren syndrome. Her medication history was negative, and her family history was negative for autoimmune disease. Physical examination by primary care revealed an erythematous scaly rash with plaques and papules on the neck and back (Figure 1). The patient presented again to primary care 2 days later with swollen, painful, discolored digits (Figure 2) and a stiff, sore neck.
FIGURE 2. Pink hands with edematous phalanges 2 days after vaccination.
Laboratory results were positive for anti–Sjögren syndrome–related antigens A and B. A complete blood cell count; comprehensive metabolic panel; erythrocyte sedimentation rate; and assays of rheumatoid factor, C-reactive protein, and anti–cyclic citrullinated peptide were within reference range. A biopsy of a lesion on the back showed psoriasiform dermatitis with confluent parakeratosis and scattered necrotic keratinocytes. There was superficial perivascular inflammation with rare eosinophils (Figure 3).
FIGURE 3. A, Histopathology of one of the lesions on the back showed mainly epidermal and superficial dermal involvement (H&E, original magnification ×40). B, Psoriasiform dermatitis with confluent parakeratosis and scattered necrotic keratinocytes also were noted (H&E, original magnification ×400).
The patient was treated with a course of systemic corticosteroids. The rash resolved in 1 week. She did not receive the second dose due to the rash.
Two mRNA COVID-19 vaccines—Pfizer BioNTech and Moderna—have been granted emergency use authorization by the US Food and Drug Administration.6 The safety profile of the mRNA-1273 vaccine for the median 2-month follow-up showed no safety concerns.3 Minor localized adverse effects (eg, pain, redness, swelling) have been observed more frequently with the vaccines than with placebo. Systemic symptoms, such as fever, fatigue, headache, and muscle and joint pain, also were seen somewhat more often with the vaccines than with placebo; most such effects occurred 24 to 48 hours after vaccination.3,6,7 The frequency of unsolicited adverse events and serious adverse events reported during the 28-day period after vaccination generally was similar among participants in the vaccine and placebo groups.3
There are 2 types of reactions to COVID-19 vaccination: immediate and delayed. Immediate reactions usually are due to anaphylaxis, requiring prompt recognition and treatment with epinephrine to stop rapid progression of life-threatening symptoms. Delayed reactions include localized reactions, such as urticaria and benign exanthema; serum sickness and serum sickness–like reactions; fever; and rare skin, organ, and neurologic sequelae.1,6-8