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

Taverniti, Valentina; Martinez, Ines; Tavazzani, Beatrice; Baeza-Martínez, Carlos; López-Garcia, Francisco; Carazo-Díaz, Carmen; Santos, Juan Aguera; Villena, Julio; Salva, Susana; Taranto, María Pía; Álvarez, Susana; Font, Graciela; Navarro-López, Vicente

doi:10.3390/microorganisms14061270

Open AccessArticle

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

by

Valentina Taverniti

^1,*,

Ines Martinez

¹,

Beatrice Tavazzani

¹,

Carlos Baeza-Martínez

²

,

Francisco López-Garcia

³,

Carmen Carazo-Díaz

⁴,

Juan Aguera Santos

^5,*,

Julio Villena

⁶

,

Susana Salva

⁶

,

María Pía Taranto

⁶,

Susana Álvarez

⁶,

Graciela Font

⁶ and

Vicente Navarro-López

⁵

¹

Sacco Srl, Alessandro Manzoni Street, 29/A, 22071 Cadorago, Italy

²

Servicio de Neumología, Hospital Universitario de Elche, 03203 Alicante, Spain

³

Servicio de Medicina Interna, Hospital Universitario de Elche, 03203 Alicante, Spain

⁴

Applied Statistical Methods in Medical Research Group, Catholic University of Murcia (UCAM), 30107 Murcia, Spain

⁵

Human Microbiome Research Group, Universidad Católica San Antonio de Murcia (UCAM), 30107 Murcia, Spain

⁶

Reference Center for Lactobacilli [CERELA-CONICET], Chacabuco 145, San Miguel de Tucumán T4000ILC, Argentina

^*

Authors to whom correspondence should be addressed.

Microorganisms 2026, 14(6), 1270; https://doi.org/10.3390/microorganisms14061270

Submission received: 8 May 2026 / Revised: 29 May 2026 / Accepted: 1 June 2026 / Published: 4 June 2026

(This article belongs to the Special Issue Probiotics and Their Health Benefits)

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Abstract

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.

Keywords: probiotics; immune system; WURSS-21; common cold; gut-lung axis

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MDPI and ACS Style

Taverniti, V.; Martinez, I.; Tavazzani, B.; Baeza-Martínez, C.; López-Garcia, F.; Carazo-Díaz, C.; Santos, J.A.; Villena, J.; Salva, S.; Taranto, M.P.; et al. Randomized, Double-Blind, Placebo-Controlled Clinical Trial Assessing the Efficacy of Lacticaseibacillus rhamnosus CRL 1505 in Preventing Upper Respiratory Tract Infections in Healthy Adults. Microorganisms 2026, 14, 1270. https://doi.org/10.3390/microorganisms14061270

AMA Style

Taverniti V, Martinez I, Tavazzani B, Baeza-Martínez C, López-Garcia F, Carazo-Díaz C, Santos JA, Villena J, Salva S, Taranto MP, et al. Randomized, Double-Blind, Placebo-Controlled Clinical Trial Assessing the Efficacy of Lacticaseibacillus rhamnosus CRL 1505 in Preventing Upper Respiratory Tract Infections in Healthy Adults. Microorganisms. 2026; 14(6):1270. https://doi.org/10.3390/microorganisms14061270

Chicago/Turabian Style

Taverniti, Valentina, Ines Martinez, Beatrice Tavazzani, Carlos Baeza-Martínez, Francisco López-Garcia, Carmen Carazo-Díaz, Juan Aguera Santos, Julio Villena, Susana Salva, María Pía Taranto, and et al. 2026. "Randomized, Double-Blind, Placebo-Controlled Clinical Trial Assessing the Efficacy of Lacticaseibacillus rhamnosus CRL 1505 in Preventing Upper Respiratory Tract Infections in Healthy Adults" Microorganisms 14, no. 6: 1270. https://doi.org/10.3390/microorganisms14061270

APA Style

Taverniti, V., Martinez, I., Tavazzani, B., Baeza-Martínez, C., López-Garcia, F., Carazo-Díaz, C., Santos, J. A., Villena, J., Salva, S., Taranto, M. P., Álvarez, S., Font, G., & Navarro-López, V. (2026). Randomized, Double-Blind, Placebo-Controlled Clinical Trial Assessing the Efficacy of Lacticaseibacillus rhamnosus CRL 1505 in Preventing Upper Respiratory Tract Infections in Healthy Adults. Microorganisms, 14(6), 1270. https://doi.org/10.3390/microorganisms14061270

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

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