Inclusion Criteria:
- Male subjects between 18 and 49 years of age or female subjects between 18 and 55 years of age who provided informed consent.
- Women with negative pregnancy test.
- Women of childbearing potential must use an acceptable method of contraception.
- Cardiac enzymes within ULN.
- White blood cells ≥ 2500/mm3 and < 11,000/ mm3.
- Absolute neutrophil count ≥ 1000/mm3.
- Adequate renal function.
- Adequate hepatic function.
- Negative hepatitis B surface antigen (HBsAg) and hepatitis B core antibody (anti-HBc).
- Negative antibody test to hepatitis C virus (HCV).
- Negative urine glucose by dipstick or urinalysis.
- Normal 12-lead electrocardiogram.
- Availability for follow-up during the study.
Groups 1 and 3 (All vaccinia-naïve subjects) additionally:
- No history of known or suspected previous smallpox vaccination.
- No detectable vaccinia scar.
- No military service prior to 1989 or after January 2003.
Groups 2 and 4 (All previously vaccinated subjects) additionally:
- History of at least one previous smallpox vaccination
- Time since most current smallpox vaccination > 10 years.
Groups 1 and 2 (All HIV Infected subjects) additionally:
- Documented HIV-1 infection
- Plasma HIV-1 RNA level < 400 copies/mL at screening.
- CD4 cells ≥ 350/µL
- Haemoglobin ≥ 9.0 g/dL.
- Platelets ≥ 100,000/mm3.
- AST (SGOT), ALT (SGPT) and alkaline phosphatase ≤ 3 x ULN
Groups 3 and 4 (All Healthy subjects) additionally:
- Negative ELISA for HIV.
- Haemoglobin >11 g/dL.
- Platelets ≥ 140,000/mm3.
- AST (SGOT), ALT (SGPT) and alkaline phosphatase without clinically significant findings
Exclusion Criteria:
- Pregnant or breast-feeding women.
- Uncontrolled serious infection i.e. not responding to antimicrobial therapy.
- History of any serious medical condition (other than HIV infection).
- History of or active autoimmune disease.
- Known or suspected impairment of immunologic function (other than HIV infection).
- History of malignancy.
- History or clinical manifestation of clinically significant and severe haematological, renal, hepatic, pulmonary, central nervous, cardiovascular or gastrointestinal disorders.
- Clinically significant mental disorder not adequately controlled by medical treatment.
- Any condition which might interfere with study objectives.
- History of coronary heart disease, myocardial infarction, angina, congestive heart failure, cardiomyopathy, stroke or transient ischemic attack, uncontrolled high blood pressure, or any other heart condition under the care of a doctor.
- History of an immediate family member with onset of ischemic heart disease before age 50.
- 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.
- History of chronic alcohol abuse and/or intravenous drug abuse.
- History of allergic disease or reactions likely to be exacerbated by any component of the vaccine.
- Known previous allergic reaction to immunoglobulins.
- Known allergies to cidofovir or probenecid.
- History of anaphylaxis or severe allergic reaction.
- Acute disease (illness with or without a fever) at the time of enrollment.
- Temperature >100.4°F at the time of enrollment.
- Subjects undergoing treatment for tuberculosis infection or disease.
- Having received any vaccinations or planned vaccinations with a live vaccine within 30 days prior or after study vaccination.
- Having received any vaccinations or planned vaccinations with a killed vaccine within 14 days prior or after study vaccination.
- Chronic administration of immuno-suppressant or immune-modifying drugs.
- Post organ transplant subjects whether or not receiving chronic immunosuppressive therapy.
- Administration or planned administration of immunoglobulins and/or any blood products.
- Use of any investigational or non-registered drug or vaccine.