Answer:
A 'vaccine' is a biological preparation that improves
immunity to a particular disease.
Vaccine can be prophylactic or the aphetic. An English
physician, Edward Jenner (1749-1823) observed that people who suffered cowpox
(a mild disease) did not acquire smallpox, (a more severe disease). Jenner
decided to test his observations about cowpox and smallpox.
He took some pus with a sterile needle from the cowpox
rashes of an infected girl and injected it into scratches made in the skin of
an uninfected boy, who soon got cowpox. After he recovered, Jenner injected the
boy's arm with pus from the spots of a person suffering from smallpox. Luckily,
the body did not get smallpox and Jenner's experiment was successful.
Thus, Jenner made the first vaccine against smallpox using
the microbes of cowpox, a similar but less severe disease. The modern term
'vaccination' comes from the Latin words vacca which means cow and vaccinia
meaning cowpox.
The second generation of vaccines was introduced in 1880s
by Louis Pasteur who developed vaccines for chicken pox, cholera and anthrax.
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