To assess the impact of SQ SLIT-tablets (SQ Grass SLIT-tablet and SQ HDM SLIT-tablet) in Danish and Swedish allergic rhinitis (AR) patients, with or without asthma, between 2007-2020.

Allergic rhinitis (AR) is an inflammatory disorder, characterised by pruritus, sneezing, rhinorrhoea, and nasal congestion. It is one of the most common disorders worldwide, with an estimated global prevalence of 10-30%. AR is a chronic and progressive disease, as the underlying respiratory allergy can progress into allergic asthma. The prevalence of asthma in patients with AR is high and estimated between 10-40%. The presence of AR commonly exacerbates asthma, increasing the risk of asthma exacerbations, emergency visits and hospitalisations for asthma.

Recently, the high-quality retrospective cohort REACT study (ClinicalTrial.gov: NCT04125888) found that allergy immunotherapy (AIT) was associated with long-term reduction in AR medication use as well as significant reductions in both controller and reliever asthma medication and concurrent lower risk of asthma exacerbation and pneumonia in subjects with pre-existing asthma. The SQ sublingual immunotherapy (SLIT)-tablets have robust evidence from randomised controlled trials (RCTs), but real-world evidence (RWE) is needed to complement the findings from RCTs by looking at e.g. longer time horizons and broader patient populations. As the REACT study was not designed to specifically look at evidence-based AIT treatments like the SQ SLIT-tablets, the real-world effectiveness of SQ SLIT tablets remain to be further elucidated.

Inclusion Criteria:

AR-patients identified by dispensations of prescribed AR medications and/or ICD10-codes of AR in specialty care

For the SQ SLIT-tablet cohort:

- at least 2 dispensings within 365 days of SQ SLIT-tablets (ATC: V01AA02 and V01AA03)

For the control cohort:

- unexposed subjects will be identified from the study population of AR-patients that may be eligible to receive SQ SLIT-tablets, but have not dispensed a prescription of SQ SLIT-tablets during the index year of the case or prior to that year

Exclusion Criteria:

- allergy immunotherapy treatment with grass or HDM allergens prior to the index event

AR-patients identified by dispensations of prescribed AR medications and/or ICD10-codes of AR in specialty care