 The rate of mother-to-child transmission of hepatitis C virus HCV is only 5, even though the level of fetal exposure to the virus during pregnancy is probably much higher. How can the fetus avoid infection in so many cases? We believe the fetal immune system is not immature as has previously been thought, but instead plays an active role in protecting the fetus from infection. In this study, we aim to better understand the immune response of the fetus against maternal HCV infection. In addition, since the fetus has been shown in some cases to make an immune response against vaccines given to the mother during pregnancy, we also aim to study the fetal immune response against maternal influenza virus vaccination. We plan to study 50 HCV-positive pregnant women and their infants study group and compare them to 20 HCV-negative pregnant women and their infants control group. We estimate that approximately 30 women in the study group will have received the influenza virus vaccine. We will analyze 3 important components of mother-to-child transmission: 1 the maternal immune response against HCV and influenza virus vaccine during and after pregnancy; 2 the babys immune response to these agents at birth, 9-15 months, and 24 months; and 3 the placenta, for the presence of HCV particles or influenza virus vaccine components. The results of this study may have implications for the prevention of mother-to-child transmission of HCV and other infections, as well as for the development of novel vaccination strategies. 