Adverse events following exposure to vaccinia virus:
Following a declaration by The World Health Assembly in 1980 on the worldwide eradication of smallpox , comprehensive smallpox vaccination programs around the world were stopped. Today, >50% of the world’s population is potentially unprotected against smallpox disease . Recent warnings about the possible threat of using smallpox virus as a biologic weapon ,  prompted a resurgence of public health vaccination programs against smallpox.
In this context, and in the broader context of a need for data comparability, as discussed in the overview paper in this volume, establishing criteria for assessing adverse events following smallpox (vaccinia) vacciniation is important for clinicians administering the smallpox vaccine and appropriately treating patients with adverse events following immunization (AEFI), and also for scientists collecting, analyzing, and communicating data on AEFI. Understanding the normal changes and progression of a successful vaccination site is crucial for early recognition of complications. Based on two double-blind studies , , using different dilutions of smallpox vaccine in previously unimmunized adults, Frey et al.  noted the following descriptions about the vaccination sites (page 1266):
“Success was defined by the presence of a primary vesicle at the inoculation site seven to nine days after scarification. Other signs and symptoms of the replication of vaccinia virus include edema, tenderness, and erythema at the site of vaccination and regional lymphadenopathy. Subsequently, the vesicle evolves into a small ulcer over which a scab forms [2nd week post vaccination], ultimately leaving a small scar [3rd week post vaccination].”
Successful vaccination correlates with the laboratory demonstration of the development of a cytotoxic T-cell response, lymphocyte proliferation, neutralizing antibodies, and vaccinia virus-specific interferon-γ production. This combination of clinical and laboratory response to smallpox vaccination provides long term, and perhaps life-long immunity .
This paper lists, in Sections 2 Case definition for EV, 3 Guidelines for data collection, analysis, and presentation of EV as an adverse event following immunization, respectively, the case definition and guidelines for data collection, analysis, and presentation that the Brighton Collaboration Vaccinia Virus Adverse Events Working Group has developed for the standardized collection and assessment of eczema vaccinatum (EV) following exposure to vaccinia virus, with applicability in study settings with different availability of resources and access to health care. Widespread use of this definition with its guidelines will enable data comparability and lead to a better understanding of the adverse event.