Vaccinia is a virus that belongs to the Poxviridae family. It is best known as the virus used in the smallpox vaccine, which helped eradicate the disease. Vaccinia is similar to the smallpox virus but is less harmful to humans. The virus can cause mild skin lesions and flu-like symptoms in some individuals. However, it is generally safe and effective for vaccination purposes. The use of vaccinia in vaccines has played a crucial role in public health, preventing outbreaks of smallpox and protecting populations worldwide.