Varicella vaccine, also known as chickenpox vaccine, is a vaccine that protects against chickenpox. One dose of vaccine prevents 95% of moderate disease and 100% of severe disease. Two doses of vaccine is more effective than one. If given to those who are not immune within five days of exposure to chickenpox it prevents most cases of disease. Vaccinating a large portion of the population also protects those who are not vaccinated. It is given by injection just under the skin.