Zoster caused by varicella vaccination. After vaccination in the arm, the virus usually replicates locally (A), after which the virus travels retrograde to the dorsal root ganglia in the cervical spinal cord. The majority of cases of zoster that have been documented to be caused by vaccine virus have occurred at or near the site of the initial vaccination. In most cases, this site was the upper arm. The dermatomes which innervate the upper arm are shown in the figure. In about 5% of vaccinated children, the virus replicates to a greater extent and enters the blood stream (B). During the viremia, a rash can appear at a distant site (C); virus even can enter the head and neck region and transit into the brain (D).