A retrospective cohort study on the association between allergic rhinitis, sublingual immunotherapy, and COVID-19 symptomatology.

The impacts of allergic rhinitis (AR) and allergen-specific sublingual immunotherapy (SLIT) on coronavirus disease 2019 (COVID-19) have not been fully understood. Therefore, the aim of this study was to investigate the effects of AR and SLIT on symptoms of COVID-19 within one month after Chinese authorities adjusted their COVID-19 response measures. The study enrolled 1368 participants, including 746 AR patients and 622 controls without allergic diseases. SLIT was administered to 122 infected AR patients (AR with SLIT group), while it was not administered to the other 483 infected AR patients (AR without SLIT group). Patients’ outcomes were compared after propensity score matching (PSM). The data showed that AR played a dual role in COVID-19, acting as both a protective factor against respiratory symptoms and a risk factor increasing the likelihood of olfactory/gustatory dysfunctions and fever, compared to non-allergic individuals. Conversely, AR patients treated with SLIT presented a higher risk of respiratory symptoms but a lower risk of fever. SLIT did not influence the risk of olfactory/gustatory dysfunctions. Thus, respiratory symptoms should be considered when deciding whether to apply SLIT in AR patients with COVID-19. Additionally, the risk of fever should also be taken into account.