A Long Term, Observational Follow-Up Study of Children and Young People Who Underwent an 18-Month Course of Oral Immunotherapy Treatment for Peanut, Egg or Milk Allergy (5-15 Years Post-Treatment)

The goal of this observational study is to learn about the long-term outcomes of children and young people who underwent an 18-month course of oral immunotherapy (OIT) treatment for peanut, egg or milk allergy. It aims to: • Compare long-term changes in health-related quality of life (HRQL) at 5-15 years after stopping OIT in participants who achieved remission and those who did not. Participants will attend a single follow-up visit for: * A blood test * Skin prick test (SPT) * Allergy questionnaires

The study population will be made up of participants from four clinical trials: PEAT, PrEMO, PPOIT-001 and PPOIT-002. They are being invited to participate in the LPEM observational study to evaluate the long-term outcomes of OIT. * PEAT: Egg OIT. These participants are from the PEAT parent study (double-blind placebo-controlled randomized trial of probiotic and egg OIT). * PrEMO: Egg or Milk OIT. These participants are from the PrEMO parent study (open label study of probiotic and egg and cow's milk OIT). * PPOIT-001: Peanut OIT. These participants are from the PPOIT-001 parent study (double-blind placebo-controlled randomized trial of probiotic and peanut OIT). * PPOIT-002: Peanut OIT. These participants are from the PPOIT-002 parent study (open label study of probiotic and peanut OIT). Participants will have a blood sample taken at the visit to measure their peanut/egg/milk specific immunoglobulin E (sIgE) level. Plasma and peripheral blood mononuclear cells (PBMC) will also be stored for future analysis. A maximum of 50 milliliters (mL) of blood will be collected via venipuncture. If collection of blood via venipuncture is not possible, capillary blood via fingerprick technique will be collected instead (in which case only blood for the sIgE level will be collected, due to volume). Participants will have a skin prick test completed at the visit to measure their allergy status. The skin prick test will include the following extracts: * Positive control (histamine) * Negative control (saline) * House Dust Mite * Rye Grass * Peanut, Egg or Milk (depending on the participant's OIT treatment received in the parent study)

Inclusion Criteria: * Previous participant of PEAT, PrEMO, PPOIT-001 or PPOIT-002 parent study * Received at least one dose of OIT treatment in the parent study * Written informed consent from participant and/or parent/guardian (if below 18 years of age) Exclusion Criteria: -Have any conditions that, in the opinion of the investigator, precludes participation for reason of safety