Unfortunately, children who are not immunized pose a threat of transmission when there is disease in the community. They can pass the disease on to babies who are too young for immunizations. They also pose a threat to children with medical exemptions, including children with leukemia, who cannot be immunized because of their medical condition. For a very small percentage of children, vaccines will not “take.” These children also are put at risk. The only way we can protect them is to surround them with immunized children.