MVA, placebo and Dryvax® (Registered Trademark) will be administered by different methods. The MVA vaccine and placebo are injected into an arm muscle with a needle and syringe. The Dryvax® (Registered Trademark) vaccine is administered, as it was for many years, 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 is evidence of the development of immunity. The development of a take suggests that an individual will be protected 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.