The purpose of this clinical trial is to study a modified pox viral vector considering:

1. HIV subtype B accounts for the most frequent virus strain in Europe and North America, as well as in many parts of the world.
2. This novel vaccinia construct expressing HIV subtype B gag, pol, env and nef antigens is to be studied in humans for the first time.

Inclusion Criteria:

• male or female
• age between 18 and 55 years on the day of screening
• available for follow-up for the duration of the study (52 weeks from screening)
• able to give written informed consent
• at low risk of HIV and willing to remain so for the duration of the study low risk of HIV infection defined as: no history of injecting drug use in the previous ten years no gonorrhoea or syphilis in the last six months no high risk partner (e.g. injecting drug use, HIV positive partner) either currently or within the past six months no unprotected anal intercourse in the last six months no unprotected vaginal intercourse outside a relationship with a regular known/presumed HIV negative partner in the last six months
• willing to undergo a HIV test
• willing to undergo a genital infection screen
• if heterosexually active female, using an effective method of contraception with partner (combined oral contraceptive pill; injectable contraceptive; IUCD; consistent record with condoms if using these; physiological or anatomical sterility in self or partner) from 14 days prior to the first vaccination until 4 months after the last, and willing to undergo urine pregnancy tests prior to each vaccination
• if heterosexually active male, using an effective method of contraception with their partner from the first day of vaccination until 4 months after the last vaccination

Exclusion Criteria:

• positive for hepatitis B surface antigen, hepatitis C antibody, antibody responses to vaccinia or serology indicating active syphilis requiring treatment
• pregnant or lactating
• clinically relevant abnormality on history or examination including history of grand-mal epilepsy, severe eczema, immunodeficiency or use of immunosuppressives in preceding 3 months
• receipt of live attenuated vaccine within 60 days or other vaccine within 14 days of enrolment
• receipt of blood products or immunoglobin within 4 months of screening
• participation in another trial of a medicinal product, completed less than 30 days prior to enrolment
• history of severe local or general reaction to vaccination defined as local: extensive, indurated redness and swelling involving most of the front-lateral thigh or the major circumference of the arm, not resolving within 72 hours general: fever >= 39.5oC within 48 hours; anaphylaxis; bronchospasm; laryngeal
• HIV 1/2 positive or indeterminate on screening
• positive for hepatitis B surface antigen, hepatitis C antibody or serology indicating active syphilis requiring treatment
• grade 1 routine laboratory parameters
• unlikely to comply with protocol