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Vaccinia virus particle, coloured transmission electron micrograph (TEM). The virus is composed of a genetic core, consisting of DNA (deoxyribonucleic acid), surround by a protein coat, or capsid (pink), which is itself enclosed within a lipid envelope (purple). Vaccinia belongs to the orthopoxvirus group. It causes cowpox, a disease of cattle and humans, which produces skin lesions. It was first used by Jenner in 1796 to vaccinate against smallpox, a related but more deadly human disease. The word vaccine is derived from vaccinia.
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