Effect of Immune X on Common Cold Incidence in Healthy Adults (CELFI)

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.