Summary Purpose The long-term effects of targeted micronutrition with the holoBLG lozenge in house dust mite (HDM) allergic rhinoconjunctivitis (ARC) patients were evaluated at a follow-up visit in an allergen exposure chamber (AEC). Methods Patients who were supplemented for 3‑months with the holoBLG lozenge in a previous study with two controlled HDM-AEC challenges [visits: V1, V3] were recruited for a third AEC challenge (V5) 7–8 months after cessation of supplementation. Symptoms (nose, conjunctival, bronchial, others), well-being, and lung function parameters were recorded exactly as in the previous study. Primary endpoint was change in median Total Nasal Symptom Score (TNSS) at V5 compared to V1. Secondary endpoints included e.g. change in median Total Symptom Score (TSS) and the exploratory analysis of temporal evolution of symptom scores using linear mixed effects models. Results Of the 32 patients included in the original study, 27 could be recruited for the follow-up visit with a third AEC challenge. An improvement of 20% (p = 0.15) in the primary endpoint TNSS [V1: 2.5 (interquartile range [IQR]: 1–4), V5: 2.0 (IQR: 1–3)] was observed; 40% (p = 0.04) improvement was seen for the TSS [V1: 5.0 (IQR: 3–9), V5: 3.0 (IQR: 2–5.5)]. Analysis of temporal evolution of all symptom scores, and the personal well-being revealed sustained, clinically meaningful improvement at V5 compared to V1. No relevant lung function parameter differences were observed. Conclusions Sustained long-term reduction of TNSS (primary endpoint) and sustained long-term improvement of secondary endpoints (temporal evolution of all symptom scores and well-being) were demonstrated 7–8 months after cessation of holoBLG supplementation, indicative of a long-lasting nature of immune resilience induced by holoBLG. Trial registration The study was registered at clinicaltrials.gov (NCT04872868).