Effect of Immune X on Common Cold Incidence in Healthy Adults

The goal of this clinical trial is to learn if Immune X can help prevent common cold events in healthy adults who have a history of upper respiratory tract infections. The main questions it aims to answer are: * Does Immune X reduce the proportion of participants who experience at least one clinically confirmed common cold event during the study period? * Does Immune X affect the number, duration, and severity of common cold events? Researchers will compare Immune X to a placebo (a look-alike capsule containing inactive ingredients) to see if Immune X helps prevent common cold events. Participants will: * Take Immune X or placebo daily for 16 weeks during the winter season. * Attend study visits at the beginning and end of the study and complete questionnaires and symptom assessments throughout the study. * Record cold symptoms, medications, and other study information using a smartphone application. * Provide blood and stool samples during the study.

Inclusion Criteria: * Men and women aged 18 to 65 years. * History of at least two upper respiratory tract infections during the previous winter season. * Body mass index between 18 and 30 kg/m². * Generally healthy, as determined by the investigator. * Women of childbearing potential must have a negative pregnancy test and agree to use an effective method of contraception during the study. * Covered by French health insurance. * Able and willing to provide written informed consent. Exclusion Criteria: * Current or recent upper respiratory tract infection or COVID-19 infection within 2 weeks before enrollment. * Acute gastrointestinal infection, including gastroenteritis, within 2 weeks before enrollment. * Use of non-steroidal anti-inflammatory drugs (NSAIDs) within 2 weeks before enrollment. * Use of systemic antibiotics within 3 months before enrollment. * Receipt of any vaccination within 6 weeks before enrollment. * Surgery requiring general anesthesia within 1 month before enrollment. * History of chronic respiratory disease, including asthma or chronic obstructive pulmonary disease. * Food allergy or chronic/recurrent allergic upper airway conditions requiring regular medical treatment, including moderate to severe allergic rhinitis, hay fever, or chronic rhinosinusitis. * Acute lower respiratory tract infection within 6 months before enrollment or ongoing long COVID. * Immunodeficiency (including HIV infection) or autoimmune disease, except stable hypothyroidism. * Severe or uncontrolled chronic disease, including cancer, significant liver, pancreatic, biliary, or renal disease, inflammatory bowel disease, or cardiovascular disease requiring intensive medical management. * Untreated or inadequately controlled diabetes. * History or current diagnosis of periodontitis. * Current chemotherapy, immunosuppressive therapy, or chronic treatment with corticosteroids or opioids. * Specific diets or major dietary changes within 3 months before enrollment, including high-protein, vegan, low-calorie, or low-FODMAP diets, or participation in a weight-loss program. * Current use of dietary supplements that may affect immune or gut microbiota parameters, or discontinuation of such supplements less than 6 weeks before enrollment. * Current smoking or e-cigarette use, or smoking cessation within 6 months before enrollment. * Current drug or alcohol abuse, or a history of abuse within the previous 12 months. * Regular consumption of more than 2 alcoholic drinks per day and unwillingness to maintain stable drinking habits during the study. * Unwillingness to refrain from using over-the-counter cold remedies, nasal washes or sprays, antihistamines, corticosteroids, or NSAIDs during the study. * More than 8 hours per week of vigorous physical activity or planned major changes in physical activity during the study. * Any condition or circumstance that, in the investigator's judgment, may place the participant at unacceptable risk or interfere with study participation or interpretation of study results. * Current participation in another clinical trial or being in an exclusion period from a previous clinical trial. * Pregnant or breastfeeding. * Persons deprived of liberty, under legal protection, or unable to provide informed consent. * Individuals who have reached the regulatory compensation limit for participation in clinical research.