A mother watched with dread as a nurse inserted a tube in her baby's head. Blood streamed into the anemic 4-month-old who already has malaria, the mosquito-borne disease that kills a million African children every year. "Malaria is one of the deadliest sicknesses for children," the nurse said -- words that sent the young mother into a crumpled heap on the bed beside her wide-eyed baby boy, wrapped in a blue-and-yellow floral blanket. There is new hope, however, in this verdant area where President Barack Obama's relatives live. A vaccine that appears to be able to prevent the disease in about 50 percent of children, is now undergoing the final stage of testing. If regulators determine the vaccine is safe, it could be on the market in...