Chasing Jenner's Vaccine

Edward Jenner Cowpox virus (CPXV) is one of the earliest described members of the genus Orthopoxvirus (OPV). Historically, researchers referred to the ailment known as cowpox and even suggested that it could provide immunity against smallpox. It was Edward Jenner’s publications in 1798 and 1799 which provided the first scientific description of vaccination by detailing the efficacy of CPXV “scarification” in inducing protective immunity against challenge with variola (smallpox) virus (VARV). The common name “cowpox virus” refers to the association with pustular lesions on the teats of cows and historic zoonotic transmission of this disease to humans (milkers) through contact with infected cows. Human infections are generally mild and self-limiting with localized skin lesions healing after 3–4 weeks, however, systemic involvement and fatal outcome have been reported in immunocompromised individuals.

New analysis shows that the smallpox vaccine is known to have originated in the United Kingdom, however the vaccine strains were most closely allied to CPXV isolates from Russia and from Finland. The most likely scenario is that most of the commercially produced smallpox vaccines were not made from the original Jenner strain, but instead from isolates found in other regions of Europe.


Chasing Jenner’s Vaccine: Revisiting Cowpox Virus Classification. (2011) PLoS ONE 6(8): e23086. doi:10.1371/journal.pone.0023086
Cowpox virus (CPXV) is described as the source of the first vaccine used to prevent the onset and spread of an infectious disease. It is one of the earliest described members of the genus Orthopoxvirus, which includes the viruses that cause smallpox and monkeypox in humans. Both the historic and current literature describe “cowpox” as a disease with a single etiologic agent. Genotypic data presented herein indicate that CPXV is not a single species, but a composite of several (up to 5) species that can infect cows, humans, and other animals. The practice of naming agents after the host in which the resultant disease manifests obfuscates the true taxonomic relationships of “cowpox” isolates. These data support the elevation of as many as four new species within the traditional “cowpox” group and suggest that both wild and modern vaccine strains of Vaccinia virus are most closely related to CPXV of continental Europe rather than the United Kingdom, the homeland of the vaccine.

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