Chickenpox (also called varicella) is a common childhood disease. It is usually mild, but it can be serious, especially in young infants and adults. 1  It causes a rash, itching, fever, and tiredness. 2  It can lead to severe skin infection, scars, pneumonia, brain damage, or death.ost people who get chickenpox vaccine will not get chickenpox. But if someone who has been vaccinated does get chickenpox, it is usually very mild. They will have fewer blisters, are less likely to have a fever, and will recover faster. Top of Page.