Academic Reading — All-Types Test 6

Reading passage

How Vaccines Were Discovered **A** The idea that a controlled encounter with a disease might protect a person against its full force is far older than the modern laboratory. Centuries before anyone could see a microbe, communities in several parts of Asia and the Middle East practised a crude form of protection against smallpox. Dried material taken from the scabs of a mildly affected patient was ground to a powder and either blown into the nostrils or scratched into the skin of a healthy person. The procedure, later called variolation, usually produced a mild illness followed by lasting resistance. It was risky — a small proportion of those treated developed the full disease and died — yet the gamble seemed worthwhile in places where smallpox killed a large share of every generation. **B** Variolation reached western Europe in the early eighteenth century, carried back by travellers and diplomats who had witnessed it abroad. Its arrival provoked fierce argument. Physicians disagreed about whether deliberately infecting a well person could ever be justified, and clergymen debated whether it interfered with providence. Nevertheless the practice spread, partly because the arithmetic favoured it: the death rate from variolation was far lower than the death rate from smallpox caught by chance. What the practice lacked was any understanding of why it worked. The prevailing theories of disease still blamed foul air or an imbalance of bodily fluids, so the protection variolation conferred remained a mystery even to those who performed it. **C** The decisive step came from an English country doctor who noticed something his rural patients took for granted. Dairymaids who had caught cowpox, a mild ailment passed from cattle, seemed never to fall ill with smallpox. In the closing years of the century he tested the folk belief directly. He took fluid from a cowpox sore on a milkmaid's hand and introduced it into the arm of a young boy, who developed only a slight fever. Weeks later he exposed the same boy to smallpox material — and the child stayed healthy. Because the protective agent came from the cow, from the Latin word vacca, the doctor named his method vaccination. **D** Vaccination spread quickly, but for most of the following century it advanced by imitation rather than by theory. Doctors copied a procedure that plainly worked without knowing the mechanism behind it, and there was no way to extend the approach to other diseases, because no one knew what made cowpox and smallpox related. That gap began to close only when a new generation of investigators established that many diseases are caused by specific micro-organisms, each capable of being grown, studied and, crucially, weakened in the laboratory. Once a germ could be cultivated deliberately, it could also be tamed deliberately. **E** A French chemist turned biologist supplied the missing principle almost by accident. Studying a bacterium that caused fowl cholera, he set aside a culture over a summer holiday and returned to find it had lost most of its power to sicken the birds. Injected with this stale preparation, the chickens survived; better still, when he later challenged them with a fresh, virulent culture, they resisted it. He grasped at once that ageing had weakened, or attenuated, the microbe without destroying its ability to train the body's defences. The insight was general. It meant that vaccines need not depend on a lucky natural relative such as cowpox; a dangerous organism could be deliberately weakened and turned into a protective one. **F** From that principle the modern discipline grew. Later researchers learned to attenuate viruses as well as bacteria, to kill organisms outright while preserving the features the immune system recognises, and eventually to use only fragments of a germ rather than the whole. Each advance rested on the same foundation laid down over two centuries: that a harmless or weakened preview of an infection can prepare the body to defeat the real thing. What began as a folk gamble with smallpox scabs had become a rational technology, though one whose earliest practitioners would scarcely have recognised the science that grew from their bold experiments.