For reasons we don't understand, peanut allergy is rapidly becoming more prevalent in the Western world, now thought to be more than 2% in the US. It is usually life-long, frequently causes huge anxiety and occasionally severe anaphylactic reactions. Immune tolerance treatment is known to be at least partially effective in those who already have allergy, but what about preventing it in young infants who have never been exposed?

Researchers based in the UK and the US recruited 640 British infants between 4 and 11 months of age, who were …