Features of chronic urticaria after COVID-19 mRNA vaccine, a real-life cohort study

New onsets of chronic urticaria (CU) have been reported after repeated immunizations, mainly with the Moderna mRNA-1273 vaccine (Spikevax). This study aims to evaluate patients with CU after COVID-19 mRNA vaccination. The contribution of SARS-Cov2 infection, atopy and IgE against the vaccine was analyzed. We monitored the features of patients who developed CU after vaccination in the Canton of Vaud through two surveys conducted in 2022 and 2023. Fifty individuals with CU underwent blood tests, and their results were compared with individuals without a history of urticaria (N=135). The presence of anti-vaccine IgE was detected with basophil activation tests (BAT). We assessed anti-SARS-Cov2 humoral response, and the presence of IgEs against common respiratory allergens (Phadiatop) as a surrogate for atopy. Post-vaccination CU occurred after a median interval of 10 days and significantly more after the Spikevax booster, affecting middle-aged individuals (median 41, 66% females). In 2023, CU was still active in 53% of the cases. Inducible forms of CU, primarily dermographism, were reported in 54% (2022) and 61% (2023) of the cases. BAT positivity was not specific to CU, anti-nucleocapsid positivity, or atopy but was significantly associated with higher anti-spike neutralizing activities and younger age. Four CU patients tolerated an additional dose of mRNA vaccine with no disease exacerbation/recurrence. The spikevax booster induced anti-vaccine IgE independently of CU, the latter being not directly associated with COVID-19 infection nor atopy. The tolerance to a new booster in 4/4 patients suggests that the Spikevax vaccine indirectly triggered CU in predisposed individuals. Blood samples were collected from patients with chronic urticaria and healthy controls in PAXgene Blood RNA tubes. RNA-seq libraries were generated from the blood samples and used to perform differential gene expression analysis and pathway enrichment analyses.