Smallpox vaccine contains live vaccinia virus (not smallpox virus) to protect against smallpox. This same vaccine has been given to millions of Americans, including Service members during World War I, World War II, and until the 1980s. Between December 2002 and January 2008, more than 1.4 Million Service members received smallpox vaccination.
The vaccine is made from a virus called vaccinia, which is another “pox”-type virus related to smallpox. The vaccine helps the body develop immunity to smallpox. The vaccine does not contain the smallpox virus and cannot spread smallpox. The vaccine was successfully used to eradicate smallpox from the human population.
The vaccine virus (vaccinia) is similar to the smallpox virus (variola). Edward Jenner reported in 1796 that people given vaccinia (smallpox) vaccine become protected from smallpox. Smallpox vaccine was the very first vaccine and has been used successfully for over 200 years.
Getting smallpox vaccine before exposure will protect about 95 percent of people from getting smallpox. Vaccination within 3 days after exposure will prevent or significantly lessen the severity of smallpox symptoms in the vast majority of people. Vaccination 4 to 7 days after exposure likely offers some protection from disease or may modify the severity of disease. Vaccination after this time may not offer any benefit.
Both Dryvax and ACAM2000 are derived from the New York City Board of Health strain using a pox virus called vaccinia, but Dryvax was grown on the skin of calves and essentially freeze-dried for storage. Dryvax was licensed and approved by the FDA, in 1931 and is now in limited supply because it is no longer manufactured.
ACAM2000, Smallpox (Vaccinia) Vaccine, Live, approved by FDA in 2007, is a live vaccinia virus derived from plaque purification cloning from Dryvax®, grown in African Green Monkey kidney (Vero) cells, and tested to be free of adventitious agents.