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BACKGROUND: More than 90% of the Spanish population has been vaccinated against the SARS-CoV-2 virus in our setting. The administration of this vaccine is not contraindicated in allergic subjects; however, it is unknown whether any precaution should be taken when initiating subcutaneous allergen immunotherapy after this vaccination.

The objective of the study was to analyze the safety of subcutaneous allergen immunotherapy during the dose escalation phase in subjects sensitized to pollens or mites previously vaccinated against SARS-CoV-2.

METHODS: An observational study with retrospective data collection from protocolled patients' medical records was designed. Outpatients older than 12 years with diagnosis of pollen or house dust mite allergic rhinitis with or without bronchial allergic asthma were selected who had completed the subcutaneous immunotherapy dose escalation phase. A complete SARS-CoV-2 vaccination was required for the inclusion.

RESULTS: Three hundred and seventy-nine patients were included by 53 investigators. The mean age was 31 years old and 55,9% female. Time from last SARS-Cov-2 vaccination dose to subcutaneous immunotherapy initiation was 4.1 months (95%CI 3.8-4.4). subcutaneous immunotherapy with a pollen allergoid was administered to 135 patients (35.6%) with a total of 739 injections, while subcutaneous immunotherapy using a house dust mite allergoid was administered to 244 patients (64.4%) with a total of 1311 doses. During the dose escalation phase with the pollen allergoid, 45 patients (33.3%) suffered 93 local adverse reactions (12.6% of injections), while 17 patients (12.6%) experienced 17 systemic allergic reactions (2.3% of injections) of them 14 were World Allergy Organization Grade 1 and 3 of Grade 2. During the dose escalation phase with the house dust mite allergoid, 55 patients (22.5%) reported 133 local adverse reactions (10.1% of injections), and 7 patients (2.9%) showed 7 World Allergy Organization Grade 1 systemic reactions (0.5% of injections). No systemic reactions Grade 3 or higher were reported.

CONCLUSIONS: The well-known safety profile of the subcutaneous allergen immunotherapy using pollen or house dust mite allergoids has not been changed after the SARS-CoV-2 vaccine administration. No relevant differences in the incidence of local or systemic allergic reactions during the dose escalation phase were identified, so it is considered that the patient’s safety has not been compromised to initiate this treatment after the SARS-CoV-2 vaccine administration.