Can a bacterial immune pill prevent asthma in toddlers?

No. In 822 high-risk children, the bacterial immune pill OM-85 did not prevent wheezing illness. Over the three years after treatment ended, 21% of children who took the drug had at least one wheezing chest illness, compared with 18% of children who took a placebo.

OM-85 is a capsule made from killed bacteria, the kind that cause common airway infections. The idea behind it is training. Give a baby’s immune system a regular, harmless look at bacterial fragments, and it may learn to respond to real infections without the overreaction that turns a cold into a wheezing attack. That theory came out of good science, and earlier smaller studies had been encouraging enough that the US National Heart, Lung, and Blood Institute paid for a proper test.

That test was the ORBEX trial, and it is the reason this result matters. It was designed the way you would want a prevention trial designed, and it came back negative.

What the data show

Researchers enrolled 822 children between January 2017 and November 2020, splitting them evenly, 411 to OM-85 and 411 to placebo. All of them were at increased risk of asthma because they had eczema, a parent with asthma, or a brother or sister with asthma. They were young when they started, with an average age of 11.8 months.

During the three-year observation period after the drug was stopped, 132 children had at least one wheezing chest illness. That was 71 of 342 children in the OM-85 group, or 21%, and 61 of 339 in the placebo group, or 18%. So the children on the active drug wheezed slightly more often, by about 3 in every 100, not less. The gap was too small and too uncertain to mean anything, but the direction alone tells you there was no hidden benefit sitting in the data.

The formal comparison agreed. Time to a child’s first wheezing illness worked out to about a 16% higher risk in the OM-85 group (hazard ratio 1.16), but the true value could plausibly sit anywhere from about 18% lower to about 64% higher (95% CI 0.82 to 1.64). That range covers “helps a bit,” “no effect,” and “harms a bit,” which is another way of saying the trial found nothing. There was roughly a 1 in 3 chance of seeing a difference this size by luck alone (p = 0.35), nowhere near the threshold for a real effect.

Dr. Kumar’s Take

A clean negative trial is worth more than most people give it credit for. Bacterial lysates are already sold in much of the world, and parents of wheezy toddlers are an easy audience, because watching your child struggle to breathe makes almost any option sound reasonable. Now there is a large, blinded, placebo-controlled answer in the highest-risk group you could pick, and the answer is that it does not work for this purpose.

The safety picture was reassuring. The most common side effects were fevers, coughs, and colds, and those happened at the same rate in both groups. So this is not a story about a dangerous drug. It is a story about an ineffective one for this particular goal, which still matters, because every month of dosing costs money and effort that could go somewhere useful.

The honest scientific message is that the immune-training idea did not translate. That does not mean early-life immune exposure is irrelevant to asthma. It means bacterial lysates are not efficacious for the primary prevention of asthma-like symptoms during the preschool years.

How the trial was run

The design leaves little room for doubt. Children aged 6 to 18 months were randomly assigned at 11 academic medical centers across the United States to receive either 3.5 mg of OM-85 or placebo by mouth, 10 days each month, for 24 months. The active drug and the placebo came in identical openable capsules, and staff, investigators, and families were all kept unaware of who got what. Randomisation was balanced by sex, age group, family history of asthma, and site.

Then the trial did something unusual and valuable. Instead of measuring results while children were still taking the capsules, it waited. The main outcome was the time to the first wheezing chest illness during the 36 months after the drug was stopped. That is the right question for a prevention drug. Anyone can suppress symptoms while a treatment is active. The claim being tested here was that early immune training would leave a lasting mark, and three years of follow-up off the drug is a fair way to check.

Retention held up reasonably well for a five-year study in toddlers, with 681 children finishing the 24-month treatment period and 596 finishing the 36-month observation period.

Practical Takeaways

If you have been offered a bacterial lysate such as OM-85 to keep a young child from developing asthma or recurrent wheezing, this trial says it does not achieve that, even in children at the highest risk.
Children who wheeze still need real treatment for the episodes themselves, and this trial changes nothing about that. Every child in it received usual care for wheezing illness under US guidelines.
Known eczema, a parent with asthma, or a sibling with asthma does raise a young child’s risk, and that is worth discussing with a paediatrician even though no pill currently prevents the outcome.

FAQs

What is a bacterial lysate, and is it a vaccine?

A bacterial lysate is made by breaking apart bacteria and packaging the fragments, in this case into a capsule that is swallowed rather than injected. It is not a vaccine in the usual sense, because it is not aimed at making antibodies against one specific germ. The intent is broader, to give the immune system repeated practice with bacterial material so it responds more calmly to airway infections later. OM-85 was given here at 3.5 mg for 10 days a month over two years, which is a substantial exposure by any measure.

Does this mean OM-85 is useless for everything?

This trial answers one question: whether OM-85 given in infancy prevents wheezing chest illnesses in children at high risk of asthma. It does not. The trial was not designed to test the drug for other uses or in other age groups, so results here should not be stretched to cover them. What it does close off is the biggest and most heavily promoted claim, that early bacterial lysate treatment can change the course of asthma risk. Five years of follow-up in 822 children is about as direct a test of that idea as anyone is likely to run.

Why did the researchers wait three years after stopping the drug to measure the result?

Because prevention and suppression are different claims. A drug that only works while you are taking it is a treatment, not a prevention strategy, and the whole premise of early immune training is that it leaves a durable change behind. Measuring the first wheezing illness during 36 months off the drug tests that durable change directly. It is a harder standard to meet, and OM-85 did not meet it.

Bottom Line

The ORBEX trial gave 822 infants at high risk of asthma either OM-85 or a placebo for two years, then watched them for three more. Wheezing chest illnesses occurred in 21% of the treated children and 18% of the placebo children, with no meaningful difference in how quickly the first episode arrived (hazard ratio 1.16, 95% CI 0.82 to 1.64). Side effects were no more common on the drug than on placebo. The conclusion is straightforward: bacterial lysates do not prevent asthma-like symptoms in the preschool years, and the search for something that does is still open.

Read the full study