Background: An innovation to better manage cat-allergic patients utilises anti-Fel d 1 IgY antibodies to neutralise Fel d 1 after its production by the cat. However, there is no published study showing its clinical efficacy in humans in a home setting. A longitudinal, open-label, proof-of-concept study was carried out to approach clinical efficacy of the cat food in cat-allergic patients. Methods: After a baseline evaluation, the cats ate only the cat food for the following 4 months. Daily evaluation of efficacy was performed for 2 weeks at baseline and after 1, 2 and 3 months of intervention for periods of 2 weeks. The MASK-air app was used daily to assess symptoms, work productivity and medications. Results: Of the 49 patients screened, 42 were followed up and 33 (78.5%) reported MASK-air data at all 3 evaluation periods. The primary end point (visual analogue scale [VAS] for global allergy symptoms) was significantly improved (p < 0.0001). All symptoms (VAS nose, eye, and asthma), VAS work and the combined symptom-medication score significantly improved after 1 month. The percentage of uncontrolled days (VAS>20/100) decreased from 64% at baseline to 35% at 1 month (p < 0.0001) and 14% at 3 months. A sensitivity analysis in patients with uncontrolled disease at baseline found similar results. Discussion: A cat diet containing anti-Fel d 1 antibodies was able to (i) show decreased allergic symptoms and related outcomes, (ii) inform the design and feasibility of future studies with a control arm and (iii) estimate the sample size of the study.
