How old does a new born have to be to get his second hepititis shot?

4weeks later. Second dose can be given after a minimum of 4 weeks interval.
Bet. 1 & 2 mos. The second dose of Hepatitis B Vaccine is typically given 4-8 weeks after the first dose.
4 weeks. There must be at least 4 weeks spacing between the 1st and 2nd shots. If your child received the first dose in the hospital after birth, then the soonest your child could receive it would be at one month of age.