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

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Abstract
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. This study aimed to extend these observations to younger children. 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. 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. 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.