Who benefits most from probiotics for respiratory infections?
Children appear to benefit the most. In a 2025 randomized trial of 128 children aged 28 days to 4 years with fever and upper respiratory infection, those given a daily probiotic mixture (Bifidobacterium breve M-16V, Bifidobacterium lactis HN019, and Lactobacillus rhamnosus HN001) had fever for a median of 3 days versus 5 days in the placebo group — a 2-day reduction [1][3]. Another 2025 study of 64 children with recurrent infections found that only 28% of those taking probiotics had another infection within 3 months, compared to 53% in the control group [4]. A larger systematic review of 32 randomized trials in children and adolescents (over 8,400 participants) reported that 78% of the studies found probiotics reduced infection rates, with Lactobacillus rhamnosus GG (LGG) strains showing particular promise in daycare settings [13].
Overweight and obese adults also seem to gain extra protection. A 2021 placebo-controlled trial found that overweight/obese adults taking probiotics experienced a 27% reduction in upper respiratory infection symptoms, with even greater benefits for those aged 45+ or with a BMI of 30 or higher [10]. This is important because this group is at higher risk for severe viral infections.
Frontline healthcare workers during the COVID-19 pandemic also saw benefits. A 2021 pilot study gave an oropharyngeal probiotic (ENT-K12) to medical staff in Wuhan and found it reduced the incidence of respiratory infections by 64.8%, cut sick days by 95.5%, and reduced medication use to zero [5].
How much can probiotics reduce infection risk and severity?
The size of the effect varies, but several studies report meaningful reductions. In a 2023 observational study of 135 people with recurrent infections, taking a multistrain probiotic for 12 weeks cut the average number of infections from 4.2 to 1.3 per year, reduced symptom severity scores by more than half (from 7.6 to 3.4), and shortened each illness from 6.1 to 3.0 days [6]. Antibiotic use also dropped from 47% to 13% [6].
A 2015 Cochrane review (the gold standard for evidence synthesis) pooled data from 12 randomized trials involving 3,720 participants and found that probiotics reduced the odds of having at least one acute upper respiratory infection by 47% (odds ratio 0.53), shortened the average episode by nearly 2 days, and reduced antibiotic prescriptions by 35% [9]. The review noted the evidence quality was low to moderate, meaning the true effect could be smaller, but the direction of benefit was consistent.
In children with recurrent infections, a 2025 study of 95 children found that a 14-day course of a multistrain probiotic prevented recurrence in 59% of cases over 6 months, with no reported side effects [11]. Another study in frequently ill children attending daycare found that those taking a multi-strain probiotic had 4.6 times fewer respiratory infections in the month after stopping the probiotic compared to the control group [8].
What are the caveats and limitations?
Not all probiotics work the same way. A 2026 systematic review and meta-analysis of 32 randomized trials found that while some strains (like Lactobacillus rhamnosus GG) consistently reduced symptom duration and antibiotic use, the pooled reduction in infection incidence was not statistically significant due to extreme variation between studies [7]. This means the type of probiotic, the dose, and the population matter a lot.
Most studies are short-term (weeks to months), so we don't know if benefits last or if long-term use is safe. A 2025 review of probiotics for recurrent infections in children noted that while many trials show benefit, there are still controversies about optimal strain, dose, and duration, and more high-quality research is needed [12].
Side effects are generally mild and uncommon. In the 2025 fever-duration trial, mild gastrointestinal issues like constipation and abdominal pain occurred at similar rates in the probiotic and placebo groups (about 12-16% for constipation) [1][3]. No serious adverse events were reported in any of the studies reviewed.
The evidence is strongest for children and for specific strains (especially Lactobacillus and Bifidobacterium combinations). For adults, the data are thinner, though the overweight/obese subgroup shows promise [10]. The 2015 Cochrane review rated the overall evidence as low to very low quality, mainly due to small sample sizes and variability in study designs [9].
About These Sources
This answer is built on 13 peer-reviewed studies — published from 2015 to 2026, 8 from 2024 or later, 3 in Q1 journals, collectively cited 112 times — selected as the most relevant from 15 studies that passed quality screening, drawn from 56 papers retrieved from a database of over 500 million.
Sources used in this answer
Probiotics and Fever Duration in Children With Upper Respiratory Tract Infections
In a randomized trial of 128 children (28 days–4 years) with fever and URTI, a probiotic mixture (B. breve, B. lactis, L. rhamnosus) reduced median fever duration from 5 to 3 days (adjusted risk ratio 0.64) with no serious side effects [1].
Development and clinical assessment of a novel probiotic candy in the prevention of respiratory infections in asthmatic children
In a randomized trial of 69 asthmatic children (7–11 years), a Bacillus coagulans probiotic candy reduced symptomatic respiratory illnesses by more than half over 2 months (0.37 vs. 0.90 episodes) and lowered salbutamol use and school absenteeism [2].
Probiotics and Fever Duration in Children With Upper Respiratory Tract Infections: A Randomized Clinical Trial.
Same trial as [1] — a 2025 JAMA Network Open RCT showing a 2-day reduction in fever duration with a specific probiotic blend in young children with URTI [3].
Role of Probiotics in the Prevention of Recurrent Upper Respiratory Tract Infections in the Pediatric Age Group
In a quasi-experimental study of 64 children with recurrent URTI, those taking probiotics had a lower recurrence rate at 3 months (28% vs. 53%, p=0.042) [4].
Oropharyngeal Probiotic ENT-K12 Prevents Respiratory Tract Infections Among Frontline Medical Staff Fighting Against COVID-19: A Pilot Study
In a pilot RCT of frontline healthcare workers during COVID-19, an oropharyngeal probiotic (ENT-K12) reduced respiratory infection incidence by 64.8%, cut sick days by 95.5%, and eliminated antibiotic/antiviral use [5].
Multistrain Probiotics and their Role in Presentation of Severity and Frequency of Upper Respiratory Tract Infection
In an observational study of 135 people with recurrent URTI, multistrain probiotics over 12 weeks reduced infection frequency from 4.2 to 1.3 per year, symptom severity by more than half, and antibiotic use from 47% to 13% [6].
The Efficacy of Probiotics in Treating Upper Respiratory Tract Infections, Allergic Rhinitis, and Chronic Rhinosinusitis: A Systematic Review and Meta-Analysis
A 2026 systematic review of 32 RCTs found that while some probiotic strains reduced URTI symptom duration and antibiotic use, the pooled incidence reduction was not significant due to high heterogeneity (I²=93%) [7].
The role of multistraine probiotics in non-specific seasonal prevention of acute respiratory infections in children with recurrent URTI in organized teams
In an open study of 93 frequently ill children (3+ years) in daycare, a multi-strain probiotic reduced infection incidence and severity, and no child in the probiotic group needed antibiotics during the observation period [10].
Cochrane Commentary: Probiotics For Prevention of Acute Upper Respiratory Infection.
A 2015 Cochrane review of 12 RCTs (3,720 participants) found probiotics reduced the odds of at least one acute URTI by 47%, shortened episodes by ~2 days, and reduced antibiotic prescriptions by 35%, though evidence quality was low to moderate [11].
Probiotics reduce self-reported symptoms of upper respiratory tract infection in overweight and obese adults: should we be considering probiotics during viral pandemics?
In a placebo-controlled trial of overweight/obese adults, probiotics reduced URTI symptoms by 27%, with greater benefit in those aged 45+ or with BMI ≥30, and effects appeared within 2 weeks [12].
Role of Multi Strain Probiotics Recurrent Respiratory Tract Infections
In a study of 95 children with recurrent RTIs, a 14-day multistrain probiotic prevented recurrence in 59% over 6 months, with breastfeeding showing a significant association with effectiveness [13].
Advancements related to probiotics for preventing and treating recurrent respiratory tract infections in children
A 2025 review of probiotics for recurrent RTIs in children concluded that probiotics reduce infection frequency and severity and decrease antibiotic use, but optimal strain, dose, and duration remain unclear [14].
The Effect of Probiotics on Prevention of Respiratory Tract Infections in Children and Adolescents: A systematic Review
A systematic review of 32 RCTs (8,415 children) found that 78% of studies reported a positive effect of probiotics on reducing RTI incidence, with LGG strains showing particular promise in daycare settings [15].