Smallpox vaccine contains live vaccinia viruses. Once administered, it evokes an immune response that protects against variola virus, the virus that causes smallpox.
Smallpox vaccine is so effective that it eradicated the natural disease from the planet.
About 95% of people are protected within 10 days of getting a single smallpox vaccination.
Smallpox vaccination up to 3 days after someone is exposed to smallpox virus will prevent or reduce the severity of smallpox in most people. Vaccination 4 to 7 days after exposure will likely offer partial protection.
Solid protection lasts for 3 to 5 years after first vaccination. Solid protection after revaccination lasts about 10 years. Partial protection lasts longer, but people need to be revaccinated if too much time has passed.
Published studies show that diluted smallpox vaccine is as effective as full-strength vaccine.
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