Randomised, controlled trial evaluating the effectiveness of Probiotic and prawn oral Immunotherapy at inducing desensitisation or tolerance in participants with Prawn Allergy compared with placebo (Probiotic and prawn Immunotherapy for treatment of Prawn Allergy: PIPA study)

INTERVENTION: Participants will be randomised 1:1 into an active (probiotic and prawn immunotherapy) or placebo arm (placebo). All participants begin the trial with a day where 4 doses or prawn powder or placebo will be administered (20 minutes apart) (either prawn powder or placebo). A single dose of 2x10^10 cfu Lactobacillus rhamnosus ATCC 53103 (or placebo) is also taken. This is mixed in water or milk and is to be given immediately prior to the prawn / placebo dosing. The dose of the probiotic (placebo) is to be taken every day and the dose remains the same for the duration of the trial. If a participant does not tolerate a dose, they will go home on the dose before they reacted. This will mean that they will have an extended build up period as extra doses will be added to the schedule (ie the remaining doses from day 1) The participants are to continue having the doses daily at home at a time suitable for them / their family. Every fortnight they will visit the hospital to increase their dose under supervision. They will be given as a mixture of capsules and sachets (depending on the dose). The participant will be required to open the capsule or sachet and mix the powder with a suitable mixing medium (soup, rice or a food the participant enjoys). The whole dose it to be eaten immediately. If a participant does not tolerate a dose, they will remain on the last dose tolerated for a further 7‐14 days and attempt the build up again. They remain on the maintenance dose for the remainder of the active phase of the trial. The active phase of the trial goes for 18 months. The participants will be required to fill in a diary every day to monitor compliance and reactions. Pharmacy also count the returned capsules / sachets to ensure compliance. CONDITION: Prawn allergy PRIMARY OUTCOME: The proportion of subjects who attain sustained unresponsiveness (at 8 weeks after end‐of‐treatment) in active and placebo groups. Participants who pass the end of treatment challenge will be re‐challenged after 8 weeks of no treatment. Those who pass the food challenge will be considered to have achieved sustained unresponsiveness, those that don't pass will not. INCLUSION CRITERIA: Confirmed diagnosis of Tiger prawn allergy as defined by a failed DBPCFC with Tiger prawn and a positive SPT or sIgE to prawn or a P monodon allergen component at screening SECONDARY OUTCOME: Prawn skin prick test (SPT) wheal size at study entry, end‐of‐treatment, and 8 weeks and 12 months after end‐of‐treatment in active and placebo groups. The proportion of subjects who are eating prawn in their diet 12 months after end‐of‐treatment in active and placebo groups. This will be captured using a follow up diary which will be given at either end of treatment (if they fail the first challenge) or at 8 weeks post end of treatment. The proportion of subjects who attain desensitisation (at end‐of treatment) in active and placebo groups. The participants will be challenged at the end of study treatment. Those that pass will be considered desensitised, those that do not, wont. To assess changes in sIgE and sIgG4 levels to prawn and prawn components (Pen m1,2,3,4) at study entry, end‐of‐treatment, and 8 weeks and 12 months after end‐of‐treatment in active and placebo groups. The serum/plasma will be stored at ‐80C for batched analysis. Serum/plasma levels of sIgE and sIgG4 against prawn will be measured by ImmunCAP (Phadia AB, Uppsala, Sweden) at MCRI, and against and prawn components (Pen m1,2,3,4) by a ELISAs at James Cook University. To compare quality of life at pre‐treatment and 12 months AFTER end‐of‐treatment in active and placebo groups. This will be captured by administering the FAQLQ‐PF