An immune-priming lysate did not prevent wheezing illness in at-risk toddlers

OM-85, a bacterial lysate taken by mouth and marketed as a way to prime a young child's immune system against respiratory infection, did not prevent the wheezing illnesses it was tested against [s1]. In the ORBEX trial, published in The Lancet on September 7, children given the drug were if anything slightly more likely than those given placebo to have a wheezing lower-respiratory illness, and the difference was not statistically significant [s1].

Wheezing lower-respiratory illnesses are common in the preschool years and are a recognised precursor of asthma. OM-85 is a lysate — a preparation of killed bacterial fragments — given in the hope that repeated low-level immune stimulation will make the airways more resilient. Smaller studies had hinted at fewer respiratory infections. ORBEX set out to test the strongest version of the claim: whether starting the drug early could stop the wheezing illnesses from happening in the first place, in the children most likely to get them.

The trial

ORBEX was a double-blind, placebo-controlled trial run at 11 academic sites in the United States in children at increased risk of asthma — those with atopic dermatitis, a parent with asthma, or a sibling aged 4 years or older with asthma [s1]. Children aged 6 to 18 months were randomly assigned 1:1 to OM-85 3.5 mg or matching placebo, taken orally for 10 days each month for 24 months, and then followed for a further 36 months off the study drug [s1]. The primary outcome was the time to a first wheezing lower-respiratory illness during that 36-month off-drug window, analysed in all randomised children [s1].

Between January 2017 and November 2020, 822 children were randomised, 411 to OM-85 and 411 to placebo; their mean age at entry was 11.8 months [s1]. Of these, 681 completed the 24-month treatment period and 596 completed the 36-month observation period [s1].

What it found

During the off-drug observation period, 132 children had at least one wheezing lower-respiratory illness: 71 (21%) of 342 in the OM-85 group and 61 (18%) of 339 in the placebo group [s1]. There was no significant difference between the groups in the time to that first illness (log-rank P=0.35; hazard ratio 1.16, 95% confidence interval 0.82 to 1.64) [s1]. The confidence interval spans 1, meaning the data are consistent with a modest benefit, no effect, or a modest harm — but the point estimate sits on the wrong side of no effect for a drug meant to help [s1].

The most frequent adverse events — fevers, coughs and colds — did not differ between the OM-85 and placebo groups [s1]. The drug was not unsafe; it simply did not do what it was given to do.

The limits

ORBEX tested a specific, high-value question and answered it cleanly, but its scope is bounded. It enrolled children already at elevated asthma risk, so it does not speak to lower-risk children [s1]. Its enrolment and follow-up ran into the COVID-19 pandemic, which reshaped respiratory-virus circulation during the study years, and attrition was non-trivial — 596 of 822 children completed the observation period [s1]. The end point was a wheezing illness, a precursor, rather than a later physician diagnosis of asthma [s1]. None of these caveats points toward a hidden benefit; they mark the edges of what a single trial can settle.

An accompanying comment on early-life primary prevention of childhood asthma set the result in the wider, largely disappointing history of attempts to head off asthma before it starts [s2].

What to watch

The value of a clean null is that it redirects effort. For a product sold on the promise of "training" a child's immune system, the burden of proof is a trial like this one, and here the promise did not hold for wheezing illness. It fits a pattern the site has traced with other immune-modulating and preventive products, from allergen immunotherapy, where the evidence is genuinely strong, to probiotics, where much of the marketing outruns the trials. The honest summary is the one ORBEX supports: in at-risk toddlers, OM-85 did not prevent wheezing lower-respiratory illness.

This article describes trial results, including a drug and its dosing, for informational purposes only. It is not medical advice or a recommendation about any product.

Sources

• [s1] Morgan WJ, et al. Use of the bacterial lysate OM-85 for the primary prevention of wheezing lower respiratory illness in preschool children: a randomised, placebo-controlled trial (ORBEX). The Lancet, published online 2026-09-07.
• [s2] Jaddoe VWV, Duijts L. Early-life primary prevention of childhood asthma. The Lancet, published online 2026-09-07.