Randomized, Double-Blind, Placebo-Controlled Clinical Trial Assessing the Efficacy of Lacticaseibacillus rhamnosus CRL 1505 in Preventing Upper Respiratory Tract Infections in Healthy Adults.

Upper respiratory tract infections (URTI) are highly prevalent worldwide. Although probiotics have shown potential in preventing URTI, evidence in healthy adults remains limited. Lacticaseibacillus rhamnosus CRL 1505 is a strain with immunomodulatory effects in preclinical studies and benefits in healthy children. Based on this evidence, a randomized, double-blind, placebo-controlled, parallel-group clinical trial was conducted in healthy adults, receiving either L. rhamnosus CRL 1505 (1 bln/day) or placebo for 12 weeks, with a 4-week follow-up. The primary endpoint was the proportion of participants experiencing URTI episodes (at least one, two, or three episode(s)). The secondary endpoints included: number and duration of URTI episodes, URTI-free time, symptom severity, use of symptomatic medication, salivary IgA levels, and safety outcomes. Results show that L. rhamnosus CRL 1505 significantly reduced the number of participants experiencing ≥3 URTI episodes at 16 weeks compared with placebo. The probiotic group experienced fewer URTI episodes per participant, a shorter cumulative duration of URTIs, and a higher URTI-free time rate. Probiotic supplementation significantly reduced the use of symptomatic medications. In conclusion, daily supplementation with L. rhamnosus CRL 1505 reduced the burden of URTI in healthy adults, specifically of those experiencing more episodes, by decreasing infection frequency, duration, and medication use.