RESUMEN
Background: Until January 2022, 8.975.458 cases of COVID-19 have been reported in Spain. In December of 2020, the European Union authorized the first mRNA vaccines against SARS-COV- 2, developed by Pfizer-BioNTech and Moderna, with two doses separated by 21 and 28 days, respectively. Reports of severe allergic reactions, including anaphylaxis, have prompted concern that the new mRNA vaccine platform has the potential to cause allergic reactions (including anaphylaxis) at a greater rate than other vaccines. Method(s): Immunization process started at Hospital Ramon y Cajal (Madrid, Spain) in January 2021. The hospital provided a form to report any adverse effect after the first or second dose of the vaccine. Until today, in our Allergy Department, we have received more than 500 patients with suspected adverse reaction to the vaccine, although the data in this publication are collected from January 2021 to September 2021. All of them were referred from different services (Occupational Risk Prevention Department, Preventive Medicine Department, General Practitioners and other specialties) by telephone, e-mail or personally at our service. Result(s): Out of the 139 vaccinated patients who reported adverse effects, 131 had a reaction with the first dose, of whom 65% were women. 51% were local reactions and 49% systemic, of which 62% were immediate reactions. We performed diagnostic tests in 55% of the patients: prick test (with macrogol, triamcinolone, dexketoprofen, methylprednisolone acetate, PEG), ID test (with triamcinolone, dexketoprofen, methylprednisolone acetate) with immediate reading and delayed reading in case of delayed reactions, epicutaneous tests (with PEG and polysorbate 80) and blood tests in systemic reactions. All diagnostic tests showed negative results. 82% of patients that reported adverse effects after the first dose tolerated the second dose of the vaccine without incidents. Only one patient had a reaction to the first and second dose despite a negative study, a 58-year- old woman who presented an urticarial rash 24 hours after administration. 8 patients, all of them women, were referred for reaction after the second dose, 87% of whom had tolerated the first dose. Conclusion(s): This single-center experience suggests that most patients who had mild reactions to the first dose of mRNA vaccines have received the second dose uneventfully or with only mild repeat reactions.