The Chickenpox vaccine debuted in the U.S. in 1995, after over 30 years of development and testing. It is approximately 85% effective in preventing Chickenpox after one dose and 99% effective after two doses. Some vaccinated children will still get Chickenpox if exposed to the “wild” virus, but their illness will be milder than if they had not received the vaccine. Side effects are minimal and rare, consisting of the occasional low grade fever or a chickenpox type rash. Some teens that get the second Varicella vaccine will get a red, warm circle around the injection site; this resolves without treatment in just a few days. The Varicella vaccine (Varivax) is recommended for all children at 12 months of age, and a booster dose at age 4-6.