As of last fall, the Canadian Pediatric Society (CPS) recommends that children should get two doses of the chickenpox vaccination as it is more effective than just one shot. Chickenpox is a highly contagious viral infection with the hallmark symptoms of extremely itchy, small blisters all over the body, as well as fever and headaches. At one time it was an accepted childhood illness, but with the advent of the chicken pox (Varicella) vaccine, it has become much less common. Chicken pox, is generally a mild illness that affects children under ten years of age. It rarely has complications in young children, although in the adult population chicken pox is often more serious.
As well as the recommendation by the CPS, the National Advisory Committee on Immunization also recommends a two-dose schedule of the Varicella vaccination, as has the American Academy of Pediatrics since 2007. It is suggested that children receive the first dose between 12 and 18 months of age and the second does between four and six years of age. Children who only got one dose as youngsters should get another one if they have never acquired chickenpox. Teens who have never had the disease should receive two shots of the vaccine.
Source: Canadian Pediatric Society Website