History
of Disease

Smallpox
Vaccine
In the late seventeen hundreds, the English country doctor Edward Jenner noticed
that dairymaids, who had contracted cowpox seemed to be protected from smallpox. (15:57) In
1796, Jenner experimented by infecting a boy with cowpox pus, then later with
smallpox pus. The boy did not contract smallpox. (15:57)
Through this experiment he demonstrated that infecting a person with a mild
or harmless virus would strengthen immunity to a similar disease-causing virus. (15:57) He
called this pus “the Vaccine Virus” – the word vaccine is
derived from the Latin word for cow. (15:57) Jenner called
this infectious material vaccine, and the procedure came to be called vaccination.
The practice of vaccination became widespread in Europe.
The material Jenner used for his vaccine probably contained cowpox virus, a
virus related to variola but not as virulent. At some time during the nineteenth
century, the virus used for smallpox vaccination ceased to be cowpox and changed
to vaccinia. (19:15) Vaccinia is in the same family as
cowpox and variola, but is genetically distinct from both. Neutralizing antibodies
induced by vaccinia vaccine are cross protective for other Orthopoxviruses,
such as monkeypox, cowpox, and variola viruses. (22:V6:4)The
origin of vaccinia, and how it came to replace cowpox virus in the vaccine
is not known.
Mass vaccination became more achievable with one of the most significant events
in the history of smallpox vaccination, the growth of the vaccine virus on
the flank of a calf in Italy, which lead to the main method for vaccine production.
With the use of vaccine produced from the flank of cows, most of Europe became
smallpox free after WWI. The virus for the vaccine was grown on the skin of
calves, sheep and water buffalo. Material from the lesions on these animals
was harvested before the pustules formed scabs in order to obtain the highest
viral load. This was then ground into a pulp and mixed with 40 to 60% glycerol. (22:V6:8) After
WWII endemic transmission was completely interrupted in Europe and North America.
With the development of a freeze-dried vaccine that was more stable in higher
temperature and humidity climates, vaccine was available for wider use throughout
the world.
The vaccine currently available in the United States was prepared in the early
1980s from calf lymph with a seed virus derived from the New York City Board
of Health strain of vaccinia. (19:15)

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