An individual's participation in the study will last up to 13 weeks. Participants will be randomized into one of two arms. The first experimental arm will consist of 20 adults with AD and 20 healthy adults. They will receive one dose of YFV-17D by subcutaneous administration in the right deltoid and receive one dose of YFV-17D placebo by transcutaneous administration in the left deltoid. The second arm will consist of 20 adults with AD and 20 healthy adults. They will receive one dose of YFV-17D placebo by subcutaneous administration in the right deltoid and receive one dose of YFV-17D vaccine transcutaneously in the left deltoid.