Effect of Mycobacterium vaccae on atopic dermatitis in children of different ages

Background Exposure to environmental microorganisms is associated with variations in the prevalence and severity of atopic diseases. We have previously shown that administration of a Mycobacterium vaccae suspension significantly reduced the severity of atopic dermatitis (AD) in children aged 5-18 years. Objectives This study aimed to extend these observations to younger children. Methods Fifty-six children aged 2-6 years with moderate to severe AD were enrolled in a randomized, double-blind, placebo-controlled trial and given one intradermal injection of either killed M. vaccae suspension or buffer solution (placebo). Skin surface area affected and dermatitis severity score were assessed before and 1, 3 and 6 months after treatment. Results Although a 38-54% reduction in surface area affected by dermatitis was noted at all time points after M. vaccae administration (P = 0.005), this improvement was not significantly different from that observed in the placebo group. Meta-analysis of this and our previous cohort (97 children aged 2-18 years) showed that M. vaccae was associated with a significant improvement in clinical severity at all ages, whereas within the placebo group, younger but not older children showed a similar improvement. Conclusions Despite a reduction in clinical severity associated with M. vaccae at all ages, no benefit could be found after administering M. vaccae to children with AD aged 2-6 years when compared with placebo. M. vaccae may offer greater benefit in children over 5 years old, whose AD appears less likely to regress spontaneously.