Hepatitis B: Formerly called serum hepatitis, it is caused by the hepatitis B virus (HBV). Approximately 10% of infected adults progress to chronic hepatitis B; 90% of newborns born to HBV infected women develop chronic infections; and young children have a 30-50% chance of developing a chronic infection. It is spread primarily through blood, unprotected sex, shared needles, and from an infected mother to her newborn during the delivery process. There is a safe vaccine for HBV.