AS, SS, LM, OA and PA did not report any COI. Funding sources None. em class=”salutation” Dear Editor, /em Within the first days of initiating mass vaccination with the novel COVID\19 vaccines several anaphylactic reactions have been reported. 1 We present two cases experiencing angioedema with or without urticarial rash after the first dose of the mRNA\1273 vaccine. period of 9?days but resolved after 7?days of treatment with oral glucocorticoids as IU1-47 well as oral antihistamines. The patient reported on no other allergies apart from a type IV\sensitization to nickel. Open in a separate window Figure 1 Urticarial rash following mRNA\1273 vaccination and skin prick test with mRNA\1273 vaccine. Urticarial skin lesions in patient #2 10?days after the first vaccination (a, b). Skin prick test in IU1-47 patient #2 showing negative results to mRNA\1273 vaccine with saline being used as negative control and histamine as positive control (c). In both patients, serological quantifications of total IgE, specific IgE to aeroallergens and tryptase levels revealed no Rabbit Polyclonal to MP68 hints of pre\existing type I\sensitizations or mast cell activation disorders (Table?1). Table 1 Two patients developing anaphylactoid reactions after mRNA\1273 vaccination and receiving omalizumab prior to second dose thead valign=”top” th align=”left” valign=”top” rowspan=”1″ colspan=”1″ /th th align=”left” valign=”top” rowspan=”1″ colspan=”1″ Patient #1 /th th align=”left” valign=”top” rowspan=”1″ colspan=”1″ Patient #2 /th /thead Age in years 2731 Sex FemaleFemale History of hypersensitivity NoneType IV (nickel) Time to systemic reaction after 1st dose 1?h10?days Symptoms AE of lips and tongue incl. dyspnoea, flushUrticarial rash with subsequent AE of tongue and upper lids Treatment i.v. CS and AHTopical and IU1-47 oral CS, oral AH Serology: total IgE, specific IgE to aeroallergens, tryptase levels (Immuno\CAP FEIA, Thermo Fisher Scientific Inc., Waltham, MA, USA)NADNAD Skin prick test (after suff. washout period) Negative for mRNA\1273Negative for mRNA\1273 BAT (mRNA\1273, PEG 2000, DMG PEG 2000; Bhlmann Laboratories AG, Sch?nenbuch, Switzerland)NegativeNegative Pretreatment with omalizumab in days to 2nd dose 27 Symptoms after 2nd dose NoneSolely localized urticaria after 8?days SARS\CoV\2 nucleocapsid\specific IgG after 2nd dose NegativeNegative SARS\CoV\2 spike\specific IgG after 2nd dose 384.00?BAU/mL 384.00 BAU/mL Neutralization titre after 2nd dose 80320 Open in a separate window Two patients who developed AE/AE with urticaria after first dose of mRNA\1273 and subsequently received IU1-47 pretreatment with omalizumab to prevent a possible anaphylactoid reaction listed with relevant clinical parameters. Antibody titre tests were performed to evaluate efficacy of mRNA\1273 vaccination: Patient sera were tested for SARS\CoV\2 nucleocapsid\specific IgG using SARS\CoV\2 IgG chemiluminescent microparticle immunoassay from Abbott performed on an ARCHITECT i2000 SR. Euroimmun Anti\SARS\CoV\2\QuantiVac\ELISA was used to measure IgG levels against SARS\CoV\2 spike S1 after the second vaccination. Neutralizing antibody titres were tested using an in\house serial dilution endpoint neutralization test performed under BSL\3 safety conditions. AE, angioedema; AH, antihistamines; BAT, basophil activation test; CS, corticosteroids; DMG, dimyristoyl glycerol; i.v, intravenous; IgE, immunoglobulin E; NAD, no abnormality detected; PEG, polyethylene glycol. After a washout period of 14?days upon cessation of systemic anti\allergic treatments, skin prick tests using residuals of the mRNA\1273 vaccine displayed no positive response (Fig.?1). In addition, flow\assisted basophil activation assays determining CD63 expression showed no sensitizations neither to polyethylene glycol (PEG) nor to the mRNA\1273 vaccine (Table?1). Thus, we found no evidence of pre\existing or newly acquired hypersensitivities to the mRNA\1273 vaccine or its components explaining the reactions in these cases. Hence, the immunological mechanisms behind the anaphylactoid reactions remain unclear. Acute allergic reactions to the novel mRNA COVID\19 vaccines have been described based on self\reports. 2 However, so far no type I\sensitization has been proven. Several publications reported on the efficacy of omalizumab, a recombinant humanized monoclonal anti\IgE antibody, in preventing hypersensitivity reactions even in cases.