The key difference between varicella and zoster is that the varicella (or chicken pox) is the primary viral infection by the varicella zoster virus whereas the zoster (or shingles) is the reactivation of the latent viral infection.
Firstly, Varicella zoster virus causes two main forms of diseases as varicella and zoster. Varicella is the primary infection by the varicella zoster virus. However, after the initial infection, varicella zoster virus can remain dormant in the dorsal root ganglia of sensory nerves and get reactivated whenever the person’s immunity weakens. Shingles or zoster refers to the reactivation of the varicella zoster virus in this manner. Therefore, varicella is the primary viral infection whereas zoster is the reactivation of the latent viral infection.
