The main objective of the Atopic Dermatitis and Vaccinia Immunization Network (ADVN) is to reduce the risk of the fatal reaction, eczema vaccinatum (EV), to the smallpox vaccination in those with atopic dermatitis (AD). Since vaccination with live vaccinia virus (VV) in individuals with AD increases the risk of EV, a yellow fever vaccine was chosen. The purpose of this study is to determine the immune response to a yellow fever vaccine in adults with AD.