Background: The ongoing COVID-19 pandemic, caused by the novel coronavirus SARS-CoV-2, represents a serious worldwide health concern. A deeper understanding of the immune response to SARS-CoV-2 will be required to refine vaccine development and efficacy as well as to evaluate long-term immunity in convalescent patients. With this in mind, we investigated the formation of SARS-CoV-2 specific BMEMORY cells from patient blood samples. Methods: A standard flow cytometry-based protocol for the detection of SARS-CoV-2 specific B cells was applied using fluorochrome-coupled SARS-CoV-2 spike (S) full-length protein. Cohorts of 26 central European convalescent mild/moderate COVID-19 patients and 14 healthy donors were assessed for the levels of SARS-CoV-2 S- specific BMEMORY cells. Results: Overall B cell composition was not affected by SARS-CoV-2 infection in convalescent patients. Our analysis of SARS-CoV-2 specific BMEMORY cells in samples collected at different time points revealed that S-protein specific B cells remain in peripheral blood at least up to 6 months after COVID-19 diagnosis. Conclusions: Detection of SARS-CoV-2 specific BMEMORY cells may improve our understanding of the long-term adaptive immunity in response to SARS-CoV-2, allowing for an improved public health response and vaccine development during the COVID-19 pandemic. Further validation of the study in larger and more diverse populations and a more extended observation period will be required.

Systemic allergic reactions to vaccines are very rare. In this study we assessed the management and outcome suspected SARS-CoV-2 vaccine hypersensitivity. We present data of 219 individuals, who experienced symptoms suspicious for an allergic reaction after the first (n=214) or the second vaccination (n=5). 195 reactions occurred after the first application of mRNA-based vaccines (157 Comirnaty®, and 38 Spikevax®) and eighteen reactions were reported after first application of a vector vaccine (Vaxzevria®). Of these 162 experienced immediate symptoms. Skin symptoms occurred in 91 cases. The most frequent cutaneous symptom was angioedema (n=45), followed by generalized urticaria (n=36) and generalized erythema/flush (n=20). 70 patients had cardiovascular symptoms, 45 showed respiratory symptoms and gastrointestinal symptoms were recorded in 14 patients. The allergological assessment of 334 individuals (219 with reactions after COVID vaccination and 115 with a history of vaccine related reactions) showed in 17% a suspicion of sensitization against the SARS-CoV-2 vaccine and/or their ingredients defined as one positive skin test and/or BAT. The majority of the SPT/IDT with the vaccines were negative. Of the 214 patients with suspected allergic symptoms after the first vaccination, 67/67 patients tolerated the re-vaccination. In this study, 334 individuals of a cohort resembling >2000 persons presenting for an allergy workup regarding SARS-CoV-2 vaccination only 45 were diagnosed in concordance with the anaphylaxis definition of the Brighton collaboration with anaphylactic immediate hypersensitivity reaction after SARS-CoV-2 vaccination. Identifiable characteristics of these patients with suspected, but also diagnosed SARS-CoV-2 vaccine hypersensitivity were female gender and the symptom angioedema. Overall, IgE-mediated hypersensitivity towards SARS-CoV-2 vaccines is extremely low and not increased in comparison to the reported hypersensitivity for other vaccines.