Efficacy and safety profile of animal dander immunotherapy: a multicentre UK studyTo the Editor,The prevalence of animal dander sensitisation has increased worldwide, with sensitisation rates in Europe as high as 26.3% to cat dander and 27.2% to dog dander.1 These aeroallergens can be found in environments such as schools, public transport or places of work, where the animals do not live and sensitisation may occur by direct or indirect contact.2 The recommended treatment for most patients in the UK is avoidance, which is not always practical or possible, particularly in public areas or places of work.Evidence for animal dander allergen specific immunotherapy (AIT) is limited, with cat dander AIT demonstrating the most consistent improvement after 12 months in a small study.3 Studies of dog dander AIT over the past 40 years have not confirmed statistically significant clinical efficacy.3,4 Other therapies described include horse dander and rat epithelium AIT.5,6In view of the limited data on animal AIT, we conducted a multi-centre review. Data on 35 patients aged 17 to 62 years (demographics in Table s1) treated with cat, dog and horse dander subcutaneous (SCIT) or sublingual (SLIT) AIT within five allergy services was analysed. All patients had confirmation of sensitisation by specific IgE or skin-prick testing. The commonest reason for AIT was workplace exposure, almost a third of which were veterinary workers (Supplementary Table s2). Efficacy was measured with different methods across different patients (Table 1). Side effects are reported in Table 2.Our data shows a higher compliance rate for SCIT patients, with 3-year completion rates at 60% compared with SLIT at 43%, accounting for 4 patients currently on treatment, which aligns with published data (Table 1). The most common reason for incomplete therapy was loss to follow-up and there were varied reasons for this (Supplementary table S3).For those who completed the full 3-year therapy, there were excellent efficacy rates for both SCIT and SLIT with 100% of patients achieving either complete or partial response (Table 2). Patient reported symptoms was the most used indicator of efficacy. A negative in-hospital cat challenge was performed in one patient and a negative home dog provocation in one patient. Efficacy was better in SCIT, with 100% complete response compared with 67% complete response in SLIT. All products established a complete response, except Oralvac cat and horse.The side effect profiles were acceptable with only one patient receiving cat dander SCIT reporting systemic side effects of rhinitis and wheeze during updosing. This patient completed updosing but did not complete maintenance therapy due to side effects. The majority of reported side effects were limited to localised reactions (Table 2). 3 SLIT patients withdrew from treatment due to undocumented side effects. Overall, 23/35 (66%) patients reported no side effects.Although numbers are small, our data demonstrates significant benefits from animal dander AIT with high efficacy rates, and side effects mainly limited to mild, localised reactions. The therapy may be most beneficial in those who are unable to avoid exposure, most commonly from workplace, or those suffering from systemic symptoms, such as asthma exacerbations when exposed to dander without the presence of the animal itself, making avoidance near impossible. Despite the benefits, animal dander AIT is used less than other inhalant allergens.One limitation of the study is that we do not have long-term follow-up data, so the durability of the response is uncertain. Adherence is also a significant issue and means to improve this should be considered.There is limited research on animal dander AIT compared with other aeroallergens, and our data has shown positive findings, although mostly with cat and dog dander. Larger cohorts are required to understand the full benefits of animal dander AIT.Table 1. Documented efficacy and compliance rates for those who completed 3 years AIT therapy.