History
of Vaccination
The principle behind vaccination was first determined by
Jenner in 1796 following the observation that milkmaids infected
with cowpox resisted infection with smallpox, i.e. that infection
with a related, but not identical virus affords protection against
the natural disease. Centuries later, that principle, applied
in a global effort, resulted in the eradication of smallpox
as a disease.
Immunity
Both antibody and cell-mediated immunity result from successful
vaccination; greater than 95% of primary vaccinees have detectable
neutralizing antibody at a titer of 1:10 or more within 1-2
weeks after immunization.
Evidence for a brisk cell-mediated immune response has also
been detected. It is believed that healing of the vaccinia infection
is associated with intact cell-mediated or T-cell and cytokine
immune competence, and that viremia is defended by an intact
antibody or B-cell immune competence.
Duration
Protection against disease following primary vaccination begins
to fade after 5 years and is probably negligible after 20 years.
In individuals who have been successfully revaccinated one or
more times, it has been found that residual immunity may persist
for 30 years or longer. Although such immunity may protect against
a fatal outcome, it may not protect against the development
of a milder form of smallpox.
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