The chickenpox vaccine is another live-virus vaccine. This means that it is possible to get the actual disease from the vaccine, albeit a milder case than that obtained from the community. Because it can possibly lead to an actual infection, the chickenpox vaccine should not be administered to pregnant women or people who have a compromised immune system.
The recommended schedule for the chickenpox vaccine is the first dose at twelve to fifteen months of age and a booster at four to six years, usually before entering kindergarten. There is some evidence that the vaccine is slightly more effective if given at fifteen months instead of at twelve months of age.
It used to be thought that a single dose of the vaccine was sufficient, but recent evidence has shown that about 15 percent of recipients are not fully protected after one dose. Thus, children over age six who only received one dose in the past should receive a booster dose at any time. The second dose has always been recommended for teenagers and adults.