Clinical progression of a smallpox postvaccination response

We present the case of a 20-year-old man with a non-necrotic, shallow, well-circumscribed ulcer on the shoulder. The patient had no significant medical history, although he noted that he was joining the military and received a smallpox vaccine injection at the same site several weeks earlier. While the differential diagnosis also included pyoderma gangrenosum, brown recluse bite, and Buruli ulcer, the patient's presentation is characteristic of a typical postvaccination progression, which is self-limited. It is important for dermatologists for be aware of this postvaccination response to avoid misdiagnosis and unnecessary workup, given that the smallpox vaccine is still administered in healthcare workers and military recruits.