Randomized, double-blind, placebo-controlled, parallel-group, clinical trial to assess the efficacy of the intake of a probiotic product composed of Lacticaseibacillus rhamnosus CRL1505 strain in reducing or preventing upper respiratory tract infections (URTIs) in a healthy paediatric population.

Randomized, double-blind, placebo-controlled, parallel-group, clinical trial.

The study aims to demonstrate the efficacy of the intake of a probiotic product composed of Lacticaseibacillus rhamnosus CRL1505 strain in reducing or preventing upper respiratory tract infections in a healthy paediatric population.

The clinical trial has an intervention period of 12 weeks and a post-treatment follow-up period of 4 additional weeks (16 weeks in total).

The study aims to demonstrate the efficacy and safety of consuming the probiotic strain Lacticaseibacillus rhamnosus CRL1505 in the prevention and reduction of the severity and duration of URTI (upper respiratory tract infections) episodes in a healthy paediatric population.

A total of 268 participants aged 3 to 12 years will be recruited and randomized into two treatment groups in a 1:1 ratio (134 participants in the PROBIOTIC GROUP and 134 participants in the PLACEBO GROUP). The two intervention groups will differ based on the treatment received: probiotic or placebo, both of which will have a similar appearance.

The study will focus on a healthy paediatric population; therefore, the exclusion criteria will eliminate children with significant acute or chronic diseases and those with an immunocompromised condition. Additionally, children receiving continuous pharmacological treatment or those who have consumed dietary supplements that could influence the study results within the four weeks prior to inclusion will be excluded. However, if these children can discontinue such treatments, they may participate in the clinical trial after a washout period. Continuous regular medication that is deemed not to influence the study outcomes regarding the efficacy of the investigational product will be allowed.

Participants will be required not to modify their diet or physical activity during the course of the study.

The inclusion process will take place during winter months, to ensure that the study coincides with the months of highest URTI incidence.

Since this clinical trial will be conducted in minors, continuous evaluation will be the responsibility of the parents. They will be instructed to complete an online questionnaire daily, which will allow data collection to assess the efficacy and safety variables.

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.