1790: Dr. Edward Jenner discovered that people given a preparation (‘vaccine’) of material from the common cattle disease, cowpox (or ‘vaccinia’), developed only a mild skin infection but when ‘vaccinated’ individuals were exposed to the deadly smallpox virus (a virus closely related to cowpox) they remained healthy.

1880: Louis Pasteur and his colleagues found that they could protect animals and people against a variety of diseases by administering injections of the infectious microorganism in an altered form.

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