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It's the only disease that humankind has successfully wiped out - and the eradication of smallpox was brought about by Edward Jenner.

He famously vaccinated a young boy against the deadly disease back in 1796.

He did this by taking some fluid from a blister the hand of a milkmaid, Sarah Nelmes, who'd contracted a similar but milder condition called cowpox, from a cow called Blossom.

He then inoculated his gardener's son, James Phipps, with the pus. Phipps was later exposed to smallpox but proved to be immune. Jenner wasn't the first to discover vaccination - but he quickly spread the word.

During the 20th century an estimated 300-500 million people died from smallpox. The characteristic rash appeared on the body and face, often leading to severe scarring and blindness.

There was cultural and religious resistance to the vaccination campaigns. But the disease - which only occurred in humans - was finally declared free from smallpox by the World Health Assembly on 8 May 1980.

There are two samples of smallpox still in existence, held in freezers under tight security in the USA and Russia.