Lack of Transmission of Vaccinia Virus

given region can be small. This would make it difficult to recruit enough controls within the small areas affected by most outbreaks, particularly within specific age strata. A control bank may therefore be more practical for use in large communitywide outbreaks, outbreaks that occur over large regions (i.e., an entire state), or in densely populated areas. Additionally, the lengthy start-up time required for questionnaire programming with a CATI system also supports the view that the CATI method may be maximally applicable in largescale investigations.