Effect of probiotics on humoral responses to COVID-19 vaccination in older adults: a randomized, placebo-controlled trial (PIRATES-COV study)
Supplementation with L. rhamnosus Rosell-11 and L. paracasei Rosell-215 did not improve anti-S1-RBD antibody responses six months after an mRNA booster dose in adults aged 65 and older.
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What the study showed
At 6 months post-vaccination, anti-S1-RBD antibody levels were comparable between probiotic and placebo groups, with similar proportions of participants showing undetectable responses. No significant between-group differences were reported in the abstract for primary or secondary outcomes.
How it was done
Double-blind RCT enrolling 592 adults aged 65–89 in Canada, randomized to a combined probiotic (6×10⁹ CFU/capsule) or placebo from 15 days before to 15 days after an mRNA booster (Pfizer or Moderna). Dried blood spot samples were collected at baseline, 3, and 6 months post-vaccination.
Risk of bias
The abstract is truncated in the results section, precluding full evaluation of secondary outcomes. The 30-day intervention window may be insufficient to sustainably modulate adaptive immunity in older adults.
What this study does NOT prove
The study does not establish immunological benefit of probiotic supplementation on mRNA COVID-19 vaccination in older adults, nor does it generalize to other strains or vaccine schedules.
In clinical practice
Available data do not support use of this specific probiotic combination to enhance COVID-19 vaccine-induced humoral immunity in older adults. Interpretation should remain cautious pending full publication.
Limitations
The abstract is truncated in the results section, precluding full evaluation of secondary outcomes. The 30-day intervention window may be insufficient to sustainably modulate adaptive immunity in older adults.
Technical appendix
Version history
- 1.0 · 2026-08-03 — Auto-generated under Evidence Standard v1.0
Paid access: structured summary from public metadata; consult the original study at the source.