Eczema vaccinatum

Eczema vaccinatum is a rare and potentially fatal severe adverse reaction to smallpox vaccination, caused by exposure to replicating live vaccinia virus in people who have ever had atopic dermatitis or another eczematous skin disorder, or in their close household contacts. The impaired epidermal skin barrier caused by eczema allows the vaccinia virus to spread widely through the skin once it establishes infection, rather than remaining localized as in a normal vaccination site. It is classified as both an infectious disease and a dermatologic condition and typically emerges five to nineteen days after exposure to vaccinia, often through household contact with a recently vaccinated person rather than direct vaccination itself. Risk factors include past or present eczema, contact with a recent smallpox vaccine recipient, filaggrin gene deficiency, and young age. Historical case-fatality rates for eczema vaccinatum ranged from about one to six percent overall, rising to roughly thirty percent in infants under two years old, if left untreated.