Inclusion Criteria:

• Ages 18-32.
• Never received smallpox vaccination.
• Read, signed and dated informed consent document.
• Availability for follow-up for the planned duration of the study two years after first immunization.
• Acceptable medical history by screening evaluation and limited physical examination.
• For women, negative serum pregnancy test at screening and negative urine or serum pregnancy test within 24 hours prior to vaccination.
• If the volunteer is female and of child bearing potential, she agrees to use acceptable contraception, and not become pregnant for at least 56 days after the last vaccination. A woman is considered of child bearing potential unless post-menopausal or surgically sterilized. [Acceptable contraception methods are restricted to effective intrauterine devices (IUDs) or licensed hormonal products with use of method for a minimum of 30 days prior to vaccination.] Women who are not sexually active must agree to use one of the acceptable contraception methods if they are of childbearing potential.
• Negative ELISA for HIV.
• ALT<1.25 times institutional upper limit of normal.
• Negative hepatitis B surface antigen and negative antibody to hepatitis C virus.
• Negative urine glucose by dipstick or urinalysis.
• Adequate renal function defined as a serum creatinine less than or equal to 1.4mg/dL for males and less than or equal to 1.2mg/dL for females; urine protein < 30 mg/dL or none or trace proteinuria (by urinalysis or dipstick); and a calculated creatine clearance greater than or equal to 80 mL/min. based on the following formulas:
• Males [(140-age in years) X weight in kg]/(72 X serum creatinine)
• Females 0.85X[(140-age in years) X weight in kg]/(72 X serum creatinine)
• ECG without clinical significance (e.g., all kinds of atrioventricular or intraventricular conditions or blocks such as complete left or right bundle branch block, AV-node block, QTc or PR prolongation, premature atrial contractions or other atrial arrhythmia, sustained ventricular arrhythmia, or 2 premature ventricular contractions (PVC) in a row, or ST elevation consistent with ischemia)
• CBC: Hemoglobin >11g/dl; White blood cells greater than 2,500 and less than 11,000/cubic mm; Platelets greater than or equal to 140,000/cubic mm.

Exclusion Criteria:

• History of immunodeficiency.
• Typical vaccinia scar.
• Known or suspected history of smallpox vaccination.
• Military service prior to 1989 or after January 2003.
• Known or suspected impairment of immunologic function including, but not limited to, clinically significant liver disease; diabetes mellitus; moderate to severe kidney impairment.
• Malignancy, including squamous cell skin cancer or basal cell skin cancer at vaccination site or history of skin cancer at the vaccination site.
• Active autoimmune disease. Persons with vitiligo or thyroid disease on thyroid replacement are not excluded.
• History of keloid formation.
• History of myocardial infarction, angina, congestive heart failure, cardiomyopathy, stroke or transient ischemic attack, or other heart condition under the care of a doctor.
• History of an immediate family member (father, mother, brother or sister) who has had onset of ischemic heart disease before age 50 years.
• Ten percent or greater risk of developing a myocardial infarction or coronary death within the next 10 years using the National Cholesterol Education Program's Risk Assessment Tool for Estimating Your 10-Year Risk of Having a Heart Attack, located at the following URL: http://hin.nhlbi.nih.gov/atpiii/calculator.asp. NOTE: This criterion applies only to volunteers 20 years of age and older.
• Abnormal troponin I.
• Use of immunosuppressive medication. Corticosteroid nasal sprays are permissible. Persons who have used topical steroid can be enrolled after their therapy is completed.
• Medical or psychiatric condition or occupational responsibilities that preclude volunteer compliance with the protocol.
• Any history of "illegal" injection drug use.
• Receipt of inactivated vaccine 14 days prior to vaccination.
• Receipt of live attenuated vaccines within 30 days of vaccination.
• Use of experimental agents within 30 days prior to vaccination.
• Receipt of blood products or immunoglobulin in the 6 months prior to vaccination.
• Acute febrile illness (greater than or equal to 100.5 degrees F) on the day of vaccination.
• Pregnant or lactating women.
• Eczema of any degree or history of eczema.
• People with atopic dermatitis, Varicella zoster, chronic exfoliative skin disorders/conditions or any acute skin disorders of large magnitude, e.g., laceration requiring sutures, burn greater than 2x2 cm.
• Household contacts/sexual contacts with, or occupational exposure to (other than minimal contact), any of the following: Pregnant women; Children <12 months of age; People with or history of eczema; People with atopic dermatitis, Varicella zoster, chronic exfoliative skin disorders/conditions or any acute skin disorders of large magnitude, e.g., laceration requiring sutures, burn greater than 2x2 cm; People with immunodeficiency disease or use of immunosuppressive medications.
• Any condition that, in the opinion of the investigator, might interfere with study objectives.
• Known allergies to or any component of MVA or MVA-BN vaccine (e.g., tris(hydroxymethl)-amino methane, sodium chloride, sucrose, dextran, L-Glutamic acid monopotassium, chicken embryo fibroblast proteins, gentamycin).
• Known allergy to egg or aminoglycoside.
• Known allergies to any component of the Dryvax® vaccine (e.g. polymyxin B sulfate, dihydrostreptomycin sulfate, chlorotetracycline hydrochloride, neomycin sulfate).
• Known allergies to any known component of the Dryvax® diluent (i.e. glycerin and phenol).
• Known allergies to any known components of vaccinia immunoglobulin (VIG), i.e. thimerosal or previous allergic reaction to immunoglobulins.
• Known allergies to cidofovir or probenecid.
• Study personnel.