Vaccinia

Vaccinia is a virus that belongs to the Poxviridae family and the Orthopoxvirus genus. It is known for its role in the development of the smallpox vaccine, the first vaccine ever developed. The virus is not naturally occurring and is instead derived from the Variola virus, the virus that causes smallpox.

History

Vaccinia was first used as a vaccine by Edward Jenner in 1796. Jenner discovered that milkmaids who had contracted cowpox, a disease similar to smallpox, did not get sick with smallpox. He hypothesized that the cowpox virus protected against smallpox and tested this theory by injecting a boy with cowpox. The boy did not get sick when later exposed to smallpox, proving Jenner's theory correct.

Characteristics

Vaccinia is a large, complex virus with a linear, double-stranded DNA genome. It replicates in the cytoplasm of the host cell and produces several proteins that interfere with the host immune response, including proteins that inhibit the host's ability to destroy the virus and proteins that inhibit the host's immune response.

Use in Vaccines

Vaccinia is used in the smallpox vaccine because it is closely related to the Variola virus but does not cause serious illness in humans. The immune response to the Vaccinia virus is similar to the response to the Variola virus, providing immunity to smallpox.

Safety and Side Effects

While the Vaccinia virus does not cause serious illness in most people, it can cause side effects. These can range from mild, such as a rash or fever, to severe, such as encephalitis or even death. The risk of serious side effects is higher in people with weakened immune systems or certain skin conditions.

See Also

• Smallpox
• Edward Jenner
• Vaccine
• Variola virus

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