Chickenpox is a very contagious illness that causes fevers and a spotty rash. It used to be common for almost every child to get chickenpox at some point.
Today a vaccine protects kids from getting chickenpox — and though it's thought of as a mild childhood disease, it can be serious or even deadly. Once you've had chickenpox, or the series of shots, you're immune from getting it again. The origin of chickenpox is uncertain: it may come from the resemblance of the rash to tiny chickpeas, or chicken pecks. Alternately, the chicken may refer to "children," or be a contrast to the more serious smallpox.