 Note: Subjects with a pre-existing chronic disease will be allowed to participate if the disease is stable and, according to the Investigators judgment, the condition is unlikely to confound the results of the study or pose additional risk to the subject by participating in the study. Stable disease is generally defined as no new onset or exacerbation of pre-existing chronic disease 6 months prior to immunization. Based on the Investigators judgment, a subject with more recent stabilization of a disease could also be eligible. 