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 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)

• Changes in HRQL scores from baseline to 5-15 years after stopping OIT in individuals who received OIT and those who received OIT placebo, as measured by FAQLQ. [Time frame: A single study visit (approximately 2 hours) will be conducted at 5-15 years after the participant completed OIT in their parent study.]
• The incidence and severity of allergic reactions (in the preceding 12 months) at 5-15 years after stopping OIT in individuals who achieved remission and those who did not, as measured by REDCap Allergen Specific Questionnaire. [Time frame: A single study visit (approximately 2 hours) will be conducted at 5-15 years after the participant completed OIT in their parent study.]
• The incidence and severity of allergic reactions (in the preceding 12 months) at 5-15 years after stopping OIT in individuals who received OIT and those who received OIT placebo, as measured by REDCap Allergen Specific Questionnaire. [Time frame: A single study visit (approximately 2 hours) will be conducted at 5-15 years after the participant completed OIT in their parent study.]
• Patterns of food ingestion (in the preceding 12 months) at 5-15 years after stopping OIT in individuals who achieved remission and those who did not, as measured by REDCap Allergen Specific Questionnaire. [Time frame: A single study visit (approximately 2 hours) will be conducted at 5-15 years after the participant completed OIT in their parent study.]
• Changes in immunological markers from baseline to 5-15 years after stopping OIT in individuals who achieved remission and those who did not, as measured by allergen specific immunoglobulin E (sIgE) blood levels. [Time frame: A single study visit (approximately 2 hours) will be conducted at 5-15 years after the participant completed OIT in their parent study.]
• Changes in immunological markers from baseline to 5-15 years after stopping OIT in individuals who received OIT and those who received OIT placebo, as measured by allergen specific immunoglobulin E (sIgE) blood levels. [Time frame: A single study visit (approximately 2 hours) will be conducted at 5-15 years after the participant completed OIT in their parent study.]