The varicella-zoster virus (VZV) is a highly contagious virus that causes two distinct diseases: chickenpox and shingles. Chickenpox typically occurs in childhood and is characterized by an itchy rash, fever, and fatigue. After the initial infection, the virus remains dormant in the body and can reactivate later in life, leading to shingles, which causes painful rashes and blisters. VZV is part of the herpesvirus family and spreads through respiratory droplets or direct contact with the rash of an infected person. Vaccination is available to prevent chickenpox and reduce the risk of shingles, making it an important public health measure.