Currently there are two immunization schedules: the 3+1 and the 2+1 schedules. In US, it is recommended to give three doses during infancy (scheduled at 2, 4, 6 month) plus one dose at 12-15 months (3+1 schedule). Since several studies have demonstrated that two doses may provide similar direct protection to three conjugate doses during infancy, it is recommended to give two doses during infancy plus a booster dose 12 months in some European countries including UK [23, 24].