Academic Reading — All-Types Test 21

Reading passage

The Discovery of Vaccines A The story of how vaccines came to exist is often told as a single moment of genius, yet it is better understood as a long conversation between careful observation and stubborn disease. For most of recorded history, epidemics of smallpox swept through communities with terrible regularity, killing a large share of those infected and scarring or blinding many who survived. Long before anyone understood what caused the illness, some societies noticed a curious pattern: a person who recovered from smallpox almost never caught it again. That single observation, repeated across many cultures over many generations, would eventually open the door to modern immunisation, though the road from noticing to explaining would prove remarkably long. B Well before European physicians took a serious interest, communities in Asia and Africa were already acting on this insight. Practitioners in several regions deliberately exposed healthy people to material taken from the sores of someone with a mild case, a procedure now known as variolation. The dried scabs were ground into powder and blown into the nose, or a small amount of fluid was scratched into the skin of the arm. The intention was to provoke a controlled, survivable bout of the disease that would grant lasting protection afterwards. It was a dangerous bargain, because a proportion of those treated developed the full illness and died, yet the death rate was strikingly lower than that of a natural outbreak, and the practice spread steadily along trade routes into the Middle East and, by the early eighteenth century, into Europe. C The decisive advance came from an observation rooted in ordinary rural life. A country doctor in the west of England noticed that milkmaids who had caught cowpox, a mild disease passed from cattle, seemed to be immune to the far deadlier smallpox. In a now-famous experiment he took fluid from a cowpox sore and introduced it into the arm of a healthy boy, then some weeks later deliberately exposed the child to smallpox. The boy did not fall ill. The physician called his method vaccination, from the Latin word for cow, and although he could not explain why it worked, he had shown that a harmless relative of a disease could be used to train the body against the dangerous one. This was a profound shift, because it replaced a frightening gamble with a comparatively safe and repeatable procedure. D For nearly a hundred years vaccination remained tied to that single lucky accident of cowpox, with no general theory that might extend it to other illnesses. The breakthrough that turned a folk remedy into a genuine science came from the laboratory rather than the farmyard. Working with the bacteria that cause chicken cholera, a French researcher happened to leave a culture unattended over a long summer holiday. When he later injected the aged, weakened sample into birds, they survived; more remarkably still, when those same birds were afterwards given a fresh and normally deadly culture, they remained perfectly healthy. He grasped that ageing the microbe had blunted its power to cause disease while preserving its ability to prompt protection. Here, at last, was a repeatable method for making a pathogen safe on purpose rather than by chance, and it could in principle be applied to almost any germ. E From this single principle the field expanded with striking speed. Researchers learned to weaken or to kill a wide range of microbes and to use the harmless versions to prime the immune system against rabies, diphtheria, tetanus and many other threats. The twentieth century added the tools to grow viruses in the laboratory, which made possible the vaccines against polio and measles that would spare millions of children across the world. What had begun as a shepherd's or a milkmaid's passing observation had become a deliberate, testable discipline with rules that could be taught. The through-line of the whole history is remarkably consistent: each advance rested on the same insight, that a mild encounter with a disease, or with something closely related to it, could shield the body against a lethal one.