Hello JEEE, In our center, we follow the 40mcg and 4 series rule. We give 40 mcg in one shot, given at one arm intramuscular. The rule is that if the HBS Titer count is more than 10 mIU/mL, there's no need to vaccinate. If the titer count is more than 1mIU/mL but less than 5mIU/mL, we should give booster doses. And when the titer count is 0.00mIU/mL, we should give the complete series. Series means the vaccine is given 0,1,2,6 months. This means 0 is the start, next dose is 1 month after start, then next is 2 months after the start, fourth dose is 6 months after first dose. I hope this helps. =)