<qa>  What is the name of the vaccine that is administered with a special forked needle?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. 