Vaccinia

Vaccinia, the cowpox virus, is closely related to the variola, or smallpox, viru. The term vaccine derives from vaccinia, because in the 18th century the English physician Edward Jennes used the vaccinia virus to develop the first successful preventive treatment for a communicable disease, smallpox, the treatment made possible the subsequent eradication of that disease.

Vaccinia is currently of special interest in genetic engineering for several reasons. Adverse reactions to the virus are rare and well understood, so it is considered safe; it is more easily transportable than most viruses, because it can be freeze dried and remain effective: Its administration is simple; and it is a large virus, making possible the use of recombinant-DNA techniques to create new vaccines. That is, genes from another virus can be spliced into vaccinia, creating a hybrid vaccine effective against both viruses.

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