Chickenpox is a contagious disease, and the only way to become immune to chickenpox without having the disease is to get the chickenpox vaccine. The varicella vaccine is given at a time, usually at the age of one year. The first injection can be given between 12 and 15 months of age, and after the first injection there is some protection against chickenpox. However, there are some people who do not get a particularly satisfactory chance of prevention without a booster shot, so a booster shot is sometimes recommended. The second booster is usually given at the age of four years, if the person is older than four years and has not had chickenpox or the chickenpox vaccine. At this point, two consecutive injections can be given, and the interval between them should be greater than four weeks, usually between four and eight weeks.