Gut Microbes. 2026 Dec 31;18(1):2699456. doi: 10.1080/19490976.2026.2699456. Epub 2026 Jul 28.
ABSTRACT
BACKGROUND: Although COVID-19 vaccination has reduced morbidity and mortality, adults aged 65 y old and older are at high risk of complications from COVID-19. The evidence suggests that probiotics may enhance immune responses when co-administered with influenza vaccination. However, few studies have evaluated the potential benefit of probiotic supplementation in this context in this high-risk population.
MATERIAL: This study was a randomized controlled trial recruiting adults between 65 and 89 y of age living in Quebec, Canada, who received an mRNA booster (Pfizer-BioNTech or Moderna). Probiotic supplementation (Lacticaseibacillus rhamnosus Rosell®-11 and Lacticaseibacillus paracasei Rosell®-215, 1x 6 x 109CFU per capsule) versus placebo was administered from 15 d pre- to 15 d post-vaccination. Participants provided dried blood spot samples at baseline, at 3- and 6-month post-vaccination. The primary outcome was the proportion of participants without detectable anti-S1-receptor binding domain (anti-S1-RBD) antibodies at 6 months post-vaccination. Secondary outcomes included longitudinal anti-S1-RBD and anti-nucleocapsid (anti-N) antibody responses across the three timepoints.
RESULTS: 592 adults were enrolled. At 6 months post-vaccination, anti-S1-RBD antibodies were comparable between groups, and the percentage of participants with undetectable antibody response in the placebo and probiotic groups (1.2% vs 1.6%) was comparable. Anti-N seropositivity was lower in the probiotic group at 6 months (OR 0.6, 95% CI 0.4-0.9; p = 0.02) and marginally lower at 3 months after adjustment. Self-reported COVID-19 infection incidence was 16.5% overall (19.1% placebo vs 13.9% probiotic; p = 0.134).
CONCLUSION: Probiotic supplementation administered around COVID-19 vaccination did not change the proportion of seronegative participants for anti-S1-RBD antibodies at 6 months. However, in the probiotic group, anti-N antibody levels were lower, while self-reported COVID-19 infections also tended to be reduced, although this difference was not statistically significant. They may be consistent with earlier control of infection and reduced exposure to the nucleocapsid antigen, but this interpretation remains speculative.
TRIAL REGISTRATION NUMBER: #NCT05195151.
PMID:42520140 | DOI:10.1080/19490976.2026.2699456
