yep CP is viral in origin and like all viral fevers notorious for prodrome features, fever, chills , weakness all these are expected, but cannot predict the severity. Severity depends on the person current state of health. If he/she has good immunity before the attack they do good. People who are on immunosuppressive drugs or sickness have it the worst. Long back before vaccines, we used unofficially advice children to get exposed to family/friends with chicken pox to get immunized while young itself, coz its bad if you get as an adult