Background: Fish is a leading trigger of food anaphylaxis. Co-sensitisation to various bony fish species is common due to similar beta-parvalbumin allergens, leading many fish-allergic individuals avoiding all types of fish. Cartilaginous fish, like sharks and rays, predominantly contain alpha-parvalbumin as the major allergen. This unique allergen profile suggests that cartilaginous fish could be a safe alternative for bony fish allergic individuals. We aimed to determine the rate of oral tolerance to gummy shark ( Mustelus antarcticus) among children with IgE-mediated bony fish allergy and evaluate the predictive value of raw gummy shark skin prick testing (SPT). Methods: Children aged 1-18 years with an IgE-mediated bony fish allergic reaction within the past 3 years underwent medical evaluation and SPTs to cartilaginous and bony fish species. All participants underwent an open challenge with 100g cooked gummy shark. Follow-up at 2 weeks and 6 months assessed ongoing tolerance and dietary incorporation. Results: All 21 children with bony fish allergy tolerated gummy shark during the challenge, despite seven (33%) children having a positive SPT (>3mm) to gummy shark (median 5mm). Six months post-challenge, 7 out of the 21 children (33%) did not incorporate gummy shark in their diet, citing taste aversion and difficulties finding a reliable source. There was one reported reaction in the community to gummy shark following the OFC. Conclusion: Bony-fish allergic children demonstrated tolerance to gummy shark. SPT to gummy shark showed limited predictive value in this cohort. Gummy shark may be a safe alternative in children with bony fish allergy.

Introduction: Children with peanut allergy are at increased risk of developing tree nut allergies, which can be severe and for most lifelong. Introduction of peanut in the first year of life can reduce the risk of peanut allergy, however, prevention strategies for tree nut allergies have not been established. We aimed to test the efficacy and safety of a novel strategy, a supervised multi-nut oral food challenge (OFC) compared to standard care for tree nut allergy prevention in infants at high risk of developing tree nut allergy, TreEAT. Methods and analysis: TreEAT is a 2-armed, open-label, randomised, controlled trial (RCT). Infants (n=212) aged 4-11months with peanut allergy will be randomised 1:1 at peanut allergy diagnosis to either a hospital-based multi-tree nut (almond, cashew, hazelnut and walnut) OFC using multi-nut butter or standard care (home introduction of individual tree nuts). All infants will be assessed at age 18months, with questionnaires and SPT to peanut and tree nuts. Peanut and tree nut OFCs will be performed as required to determine allergy status for each nut. The primary outcome is tree nut allergy at age 18 months. Secondary outcomes include peanut allergy resolution, proportion and severity of adverse events related to tree nut ingestion, number and frequency of tree nuts ingested, quality of life and parental anxiety and allergy related healthcare visits from randomisation to 18 months of age. Analyses will be performed on an intention-to-treat basis. Ethics and dissemination TreEAT was approved by the Royal Children’s Hospital Human Research Ethics Committee (#70489). Outcomes will be presented at scientific conferences and disseminated through publication. Trial registration number: ClinicalTrials.gov ID: NCT04801823