Clinical Trial to Evaluate the Efficacy of Lacticaseibacillus Rhamnosus CRL1505 in the Prevention of Upper Respiratory Tract Infections in Children

Inclusion Criteria: * Healthy children aged 3 to 12 years. * Signed Informed Consent by the parents Exclusion Criteria: * Chronic pathological conditions, such as chronic respiratory diseases (asthma, chronic bronchitis, etc.), chronic heart diseases, chronic neurological diseases (psychomotor impairment, etc.), chronic liver diseases, chronic kidney diseases, chronic gastrointestinal diseases, hematological disorders, etc., or any other disease or condition that the investigator considers to significantly affect the health of the participating child. * Metabolic disorders, such as diabetes mellitus, obesity, etc. * Immunodeficiency, including HIV infection, chronic corticosteroid treatment, etc. * Nasal polyps, nasal ulcers, or other conditions that may cause nasal obstruction. * Regular use of medications or dietary supplements that may influence the study outcomes (immunosuppressants/immunostimulants, including echinacea supplements, analgesics, anti-inflammatory drugs, antitussives/expectorants, flu preparations, decongestants, antibiotics, antihistamines, probiotics, etc.) within the 4 weeks prior to the start of the clinical trial.