Phase I/II Trial of Modified Vaccinia Virus Ankara (MVA) Vaccine Against Smallpox

This study will test the safety of an experimental vaccine called modified vaccinia virus ankara (MVA) and determine if it confers protection against the smallpox virus (variola). There is an existing vaccine, called Dryvax® (Registered Trademark), which is effective against smallpox; however, this vaccine can cause various side effects, including some that, on rare occasions, can be life-threatening. Dryvax® (Registered Trademark) has not been used in the United States since childhood vaccination was stopped in 1971, and though it is given to certain healthcare and laboratory workers, and some people in the armed forces, it is not recommended for the general population. Both the MVA and Dryvax® (Registered Trademark) vaccines are made using the vaccinia virus, which is closely related to variola. Healthy normal volunteers between 31 and 60 years of age who have been vaccinated with a smallpox vaccine more than 10 years before entering the study may be eligible for this protocol. Candidates will be screened with a medical history, physical examination, and blood and urine tests, including an HIV test and a pregnancy test for women of childbearing potential. Participants will receive MVA vaccine or placebo, followed by a dose of Dryvax® (Registered Trademark). The MVA vaccine and placebo are injected into an arm muscle with a needle and syringe. The Dryvax® (Registered Trademark) vaccine is administered with a special forked needle that is poked lightly into the skin of the upper arm, usually 15 times, in a process called scarification. When the vaccine works, a small pus-filled blister forms, followed by a scab and then scarring at the site of the vaccination. The formation of the blister and scab is called a take, indicating that the vaccine is effective and will protect against smallpox for at least a few years. If scarification does not take, it can either mean that the person already has immunity or that the vaccine did not work. Study participants will be ra