Table 1. Antiviral effects of different immunobiotics used in clinical studies.

Immunobiotics	Experimental Challenge	Study population	Study design	Antiviral outcomes	Ref
Lactobacillusrhamnosus GG	COVID-19 infection	1132 subjects tested positive for COVID-19	Double-blinded, randomised, placebo-controlled trial. Daily oral administration of LGG or placebo 28 days	Reduction of secondary infection and moderation of immunity in patients	[52]
Bifidobacterium, Lactobacillus, Enterococcus and Bacillus	COVID-19 infection	311 patientsAge ≥ 18 years	Single-center retrospective analysis 1.5 g (tablet) 28 days	Reduction of severity of disease and associated with beneficial changes in gut microbiome composition	[53]
Lactiplantibacillus plantarum KABP022, KABP023, KAPB033, Pediococcus acidilactici KABP021	COVID-19 infection	300 adult Covid19 outpatients Media age: 37 years	Single-center, quadruple-blinded, randomized trial 2 × 109 CFU/day or placebo 30 days	Reduction of nasopharyngeal viral load, lung infiltrates Increase of specific IgM and IgG level	[54]
Bifidobacterium longum Lactobacillus bulgaricus Streptococcus thermophilus	COVID-19 infection	156 patients	Randomized controlled trial 4 x 0.5 × 106 CFU, 3 times a day	Significant decrease of time to achieving a negative nucleic acid test and inflammation indexes	[55]
Bifidobacteria strains, galactooligosaccharides xylooligosaccharide, resistant dextrin	COVID-19 infection	55 patients Age ≥ 18 years	Open-label, proof-of-concept study 10 x 1011 CFU/day 28 days	Significant reduction in pro-inflammatory markers (IL-6, MCP-1, M-CSF, TNF-α and IL-1RA) compared with controls	[56]
Heat-killed Pediococcus acidilactici K15	Viral respiratory tract infections	172 children Age 3–6 years	Randomized, double-blind, placebo-controlled 5 × 1010 bacteria4 months	Duration of a fever significantly decreased sIgA level significantly higher	[57]
Lactiplantibacillus plantarum HEAL9 and Lacticaseibacillus paracasei 8700:2	Common colds	448 Age 18–70 years	Double-blind study 109 CFU/day 12 weeks	Reduction of symptom severity IFN-γ production enhancement	[58]
Bacillus spores (LiveSpo Navax)	Acute respiratory tract infections	46 children	Nasal-spraying of spores 5 × 109 spores 6 days	Symptoms improvement Reduction of load and level of pro-inflammatory cytokines	[59]
Bifidobacterium animalis subsp. lactis Bl-04 (1)	Respiratory and gastro intestinal infections	241 males; age 35 years and 224 females; age 36 years	Randomized double-blind placebo-controlled trial. 2.0 × 109 CFU/day 3–4 months	Significant decrease in respiratory illness episode compared to placebo.	[60]
Lactobacillus plantarum HEAL9 and Lactobacillus paracasei 8700:2	Common cold	131 childrenAge 1–6 years	Randomized, double blind placebo-controlled trial. 109 CFU/day 3 months	Significant decrease of symptom severity	[61]
Loigolactobacillus coryniformis K8 CECT 5711	Immune response generated by the COVID-19 mRNA vaccine	200 subjects > 60 years	Randomized, placebo-controlled, double-blind trial 3 months	Levels of IgG were significantly higher	[62]
Lactobacillus rhamnosus HN001	Acute respiratory infections	398 children Age 1–5 years	Double-blind placebo-controlled trial. 1010 CFU/day 3 months	High level of Lactobacillus Significant increase of sIgA levels in treated group	[63]
Saccharomyces cerevisiae	Cold and flu-like symptoms	116 subjects 57% femalesAge 18–94 years	Randomized double-blind placebo-controlled trial 500 mg (dried)/day 12-week	Significant decrease in incidence, no significant reduction in duration, no impact on severity of illness	[64]