How does the vaccine protect against smallpox?
The vaccine is made from a “live” virus called vaccinia, a “pox”- type virus that is related to smallpox. The vaccine produces an immune response that protects against smallpox. Routine vaccination was stopped in the U.S. in 1972. The vaccine is highly effective when given before exposure. In addition, vaccination within 3 days after exposure will completely prevent or significantly modify smallpox in the vast majority of persons. Vaccination 4 to 7 days after exposure likely offers some protection from disease or may modify the severity of disease.
