Refractory chronic spontaneous urticaria after heterologous COVID-19 booster vaccination.

Chronic spontaneous urticaria (CSU) involves recurrent, pruritic wheals lasting more than 6 weeks in response to various etiologies, including unknown causality. Though most cutaneous reactions to the COVID-19 vaccine series are self-limited and of short duration, more complex presentations including chronic spontaneous urticaria have been described. To the best of our knowledge, this is the first report of chronic spontaneous urticaria following heterologous mRNA COVID-19 booster vaccination that includes vaccination with both forms of the mRNA vaccine.