Modern vaccines date back to British doctor Edward Jenner's 1796 work immunizing children using pus from cowpox blisters.

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Some people might also contract a cowpox virus, with possibly lethal results.

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Although Warwick winces at the comparison, Boulos likens him to a latter-day Edward Jenner, who injected himself with cowpox in 1776 to further his research into a smallpox vaccine.

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He noticed that milkmaids who had developed cowpox from contact with cow udders were protected from the human form of the disease, and the cowpox virus became the basis of his vaccine.

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In 1802, after Edward Jenner published his first results claiming that scratching cowpox pus into the arms of healthy children could protect them against smallpox, a political cartoon appeared showing newly vaccinated people with hooves and horns.

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