What you may have heard: Because Hep B is most commonly transmitted through risk factors like drug use or unprotected sex, some parents wonder why this vaccine would be given to a child at all, let alone to a newborn. The reason: If you're infected as an adult with Hepatitis B, you have a less than 10 percent risk of becoming a chronic Hep B carrier, at high risk for developing liver cancer or severe liver disease, both of which can be fatal. In contrast, more than 90 percent of babies who are affected with Hepatitis B will become chronic Hep B carriers. What's more, more than half of those infected with Hep B do not have any of the common symptoms -- jaundiced (yellowed) eyes and skin, skin rash, nausea, and joint pain -- so it's sometimes impossible to know who is affected. It's estimated that up to 5,000 children in the United States are infected with Hepatitis B each year, and most of these children are born to mothers who are not infected with Hep B.