Design: parallel-arm, double-blind, placebo-controlled randomised trial with 36-month off-drug observation
Population: 822 children aged 6–18 months at increased asthma risk, 11 US academic sites
Primary outcome: time to first wheezing lower respiratory tract illness during the 36-month observation period
Effect: 71/342 (21%) vs 61/339 (18%); hazard ratio 1.16 (95% CI 0.82–1.64), log-rank p = 0.35

Bacterial lysates have been used and marketed for years on the theory that training the immature immune system reduces later wheeze. ORBEX tested it properly. Children aged 6 to 18 months at increased asthma risk — through atopic dermatitis, parental asthma, or asthma in an older sibling — were randomised at 11 US academic sites to OM-85 3.5 mg or matched placebo, given for 10 days each month for 24 months, then followed for a further 36 months off drug. The primary outcome was time to first wheezing lower respiratory tract illness during that observation period.

Of 822 randomised children, 681 completed treatment and 596 the observation period. A first wheezing illness occurred in 71 of 342 (21%) in the OM-85 group and 61 of 339 (18%) on placebo. Time to first illness did not differ (hazard ratio 1.16, 95% CI 0.82 to 1.64; log-rank p = 0.35). Fevers, coughs and colds were the commonest adverse events and did not differ between groups.

The authors' conclusion is unambiguous: bacterial lysates are not efficacious for primary prevention of asthma-like symptoms in the preschool years. That is worth stating plainly because OM-85 is widely available in India and elsewhere, often sold to exactly this group of families — children with eczema and a wheezy parent — and often at a cost that matters to them. The trial was part-funded by the manufacturer, which makes the negative result harder to dismiss rather than easier.

Do not recommend bacterial lysates for asthma prevention in at-risk young children
Tell families who are already buying it that a properly designed trial found no benefit
Redirect the conversation to what does help: tobacco smoke avoidance, indoor air quality, eczema control
Keep the risk factors themselves — eczema, parental asthma, sibling asthma — as the reason for closer follow-up

Why it matters

A widely sold preventive product has been tested in the exact population it is marketed to, and failed.

The statistics, in plain English

A hazard ratio of 1.16 with an interval of 0.82 to 1.64 is centred slightly on the side of harm and includes both a modest benefit and a modest harm — it is an absence of effect, not a hidden one. With 822 children randomised and five years of follow-up, this trial was well placed to find a clinically useful benefit and did not. The outcome was time to first wheezing illness rather than asthma diagnosis, which is the more relevant and more measurable endpoint at this age.