Your article on challenge trials raises fascinating questions, as the world seeks to address the risk of new pandemics (Should we give people diseases in order to learn how to cure them?, 31 October). It refers to Edward Jenner, who did indeed “challenge” his patient James Phipps, the eight-year-old boy he had test-inoculated with cowpox (the process that would become known as vaccination), by subsequently having him inoculated with live smallpox to ensure he was immune to the disease. However, by the time he did so in 1796, the latter technique was a widely used and highly successful procedure which, conducted safely by experienced practitioners, had a negligible risk.
Arriving in Britain from Turkey in 1721, and used for centuries in India, China and parts of Africa, inoculation involved giving healthy individuals a minute dose of smallpox virus via a scratch on the skin, leading to a mild dose of the disease and then lifelong immunity. Thomas Dimsdale, the Essex-born Quaker physician featured in my book The Empress and the English Doctor, reported having inoculated about 6,000 patients with just one death at the time he went to St Petersburg to treat Catherine the Great and her son. The empress underwent the procedure in 1768 to show her subjects how safe it was.
Jenner learned of the apparent protective property of cowpox, a cousin virus of smallpox, from farming communities in his native Gloucestershire, who found that when they underwent preventive inoculation, they were already immune. His world-changing leap forward was to formally trial the theory that a mild disease could protect against a lethal one, and then to test it by “challenging” the patient using conventional inoculation, an entirely routine preventive procedure.
Lucy Ward
Saffron Walden, Essex
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• The main picture on this article was changed on 7 November. The original image was not, as the caption said, Edward Jenner inoculating a child in 1796. It was instead a black and white version of L’innoculation by Louis Léopold Boilly which had been flipped horizontally. This has been replaced with the correct Jenner image.
