**1.1 The varicella vaccine**

In the early 1970s, Japanese researchers isolated a VZV sample from the blood of a small boy. Through serial passage in cell culture, scientists were able to successfully develop the first live attenuated varicella vaccine (Takahashi et al., 1974; Arvin, 2001; Gershon, 2001). The vaccine strain was termed the Japanese Oka varicella virus (v-Oka). By 1995, this chickenpox vaccine was introduced to the United States and quickly recommended for vaccination in all children. Since then, chickenpox incidence in the US has dramatically declined; the effectiveness of this vaccine is estimated to be between 72% and 98% (Hambleton & Gershon, 2005). Nevertheless, outbreaks of chickenpox are still ever-present. Furthermore, the vaccine may indirectly increase the occurrence of herpes zoster in the elderly population by lessening the number of natural infections, and therefore lowering the exposure to wild-type VZV that would boost natural immunity (Arvin, 2001; Galea et al, 2008; Volpi, 2005). It is also important to note that the current shingles vaccine has been shown to only reduce the risk of shingles by 50% (Oxman et al., 2005). Because of this, VZV continues to be an important public health concern. In order to improve future prevention and treatment of VZV infections, a better understanding of VZV's biology and pathogenesis is critical.
