Cutaneous reactions after COVID-19 vaccination : JAAD study
COVID-19 mRNA vaccines form the major line of protection for people in this pandemic. In December 2020, the US- Food and Drug Administration (FDA) issued emergency use authorizations for Pfizer and Moderna COVID-19 vaccines. Cutaneous reactions after these vaccines have been reported but not well characterized. A recent study evaluating the morphology and timing of cutaneous reactions after Pfizer and Moderna COVID-19 vaccines was published in the Journal of American Academy of Dermatology.
The vaccine registry collected dates for both vaccine doses, morphology of cutaneous reaction(s), timing and duration of reaction(s), and treatments. Local site reactions were defined as occurring within 3 days of first-dose and delayed large local reactions were defined as occurring 4 or more days after the first dose. Cutaneous reactions reported after vaccination with FDA-approved Pfizer or Moderna mRNA vaccines only were included.
From December 2020 to February 2021, 414 cutaneous reactions were recorded to vaccines from Moderna (83%) and Pfizer (17%). In total Delayed large local reactions were most common followed by local injection site reactions, urticarial eruptions, and morbilliform eruptions. Forty-three percent of patients with first-dose reactions experienced second-dose recurrence. Reactions like pernio/chilblains, cosmetic filler reactions, zoster, herpes simplex flares, and pityriasis rosea-like reactions were less common. No cases of anaphylaxis or other serious adverse events were reported.
Number of cutaneous manifestations after the Moderna vaccination were 343, including 267 reported after the first dose and 102 reported after the second dos me. The most common cutaneous reactions were delayed large local reactions (n = 175 first; n = 31 second dose), local injection site reaction (n = 117 first dose; n = 69 second dose), urticaria (n = 16 first dose; n = 7 second dose), morbilliform (n = 11 first dose; 7 second dose), and erythromelalgia (n = 5 first dose; n = 6 second dose).
Number of cutaneous reactions after Pfizer vaccine administration was 71, including 34 after the first dose and 40 after the second dose. The most common were urticaria (n = 8, first dose; n = 6, second dose), local injection site reaction (n = 8, first dose; n = 8, second dose), and morbilliform rash (n = 6, first dose; n = 3, second dose).
The median time from first vaccination to onset of cutaneous symptoms was 7 days which occurred in 2 clusters, one between days 1 and 3 and the other between days 7 and 8. All patients responded well to topical steroids, oral antihistamines and pain relieving medications. The reactions resolved after a median of 3-4 days without use of any antibiotics.
These data provide following salient knowledge points to clinicians that patients experiencing a delayed cutaneous arm reaction after their first Moderna dose-
tolerated the second dose without experiencing severe adverse or allergic events
the rash may recur the second time but is likely to be less severe and may develop faster
only symptomatic therapies (eg, ice/pain-relief/antihistamines/topical corticosteroids) are sufficient for treatment of reactions
Some reactions to Moderna and Pfizer vaccines were similar to that noted after SARS-CoV-2 infection like pernio/chilblains, erythromelalgia and pityriasis-rosea-like exanthems which suggests that
host immune response to the virus is being replicated by the vaccine
Some of these dermatologic manifestations of the virus are likely to be from an immune response to the virus rather than direct viral effects
To conclude most of the cutaneous reactions to COVID-19 mRNA vaccines are benign requiring only symptomatic therapy and is mostly safe from dermatological point of view.

Source-
McMahon DE, Amerson E, Rosenbach M, Lipoff JB, Moustafa D, Tyagi A, Desai SR, French LE, Lim HW, Thiers BH, Hruza GJ, Blumenthal KG, Fox LP, Freeman EE. Cutaneous reactions reported after Moderna and Pfizer COVID-19 vaccination: A registry-based study of 414 cases. J Am Acad Dermatol. 2021 Jul;85(1):46-55. doi: 10.1016/j.jaad.2021.03.092. Epub 2021 Apr 7. PMID: 33838206; PMCID: PMC8024548.