Preventing disease: from alchemy to vaccination
Preventing Disease Before Science
Prevention is better than cure — but for most of history, people could not prevent what they could not understand. Medieval and early modern attempts to stop disease relied on the same incorrect theories that shaped their understanding of its causes: miasma, divine punishment and the four humours. Only from the eighteenth century onwards did more systematic, evidence-based approaches to prevention begin to appear.
Medieval Responses to the Black Death
When the Black Death struck England in 1348, communities tried a range of preventive measures. Flagellants travelled from town to town flogging themselves, convinced that demonstrating extreme suffering would show God they had repented. Towns introduced quarantine measures, sealing infected houses and sometimes entire streets. Bonfires were lit to burn away miasma; people carried posies of sweet-smelling herbs. Alchemists sold remedies claiming to drive out poison from the body. Soothsayers and astrologers advised on auspicious dates to avoid travel. None of these worked against a flea-borne bacterial infection, but they reflected the best understanding available at the time.
Medieval plague prevention included flagellation, quarantine, burning bonfires to purify air, carrying herbs, and seeking advice from alchemists and soothsayers. All these methods were based on miasma theory or belief in divine punishment — not on knowledge of bacteria or fleas.
Inoculation: A Significant Step, c.1700
The first genuinely effective approach to preventing a specific disease came not from a European physician but from the Ottoman Empire. Inoculation against smallpox was practised in the Middle East and China before it reached Britain. In 1721, Lady Mary Wortley Montagu, wife of the British ambassador to Constantinople, introduced the practice to British society after having her own children inoculated in Turkey. She had herself survived smallpox but lost her brother to it.
Inoculation involved transferring matter from a mild smallpox pustule into a healthy person. The person usually suffered a mild form of the disease, recovered, and was thereafter protected. It was risky — a small number of those inoculated died from the procedure — but far less dangerous than catching smallpox naturally. By the mid-eighteenth century, inoculation was used across parts of Britain, particularly among the wealthy.
The most important development in disease prevention before the twentieth century was made by Edward Jenner in 1796. Jenner, a doctor working in Gloucestershire, noticed that milkmaids who caught cowpox — a mild disease affecting cattle and humans — rarely contracted smallpox. He hypothesised that the cowpox infection conferred protection against the deadlier disease. In May 1796 Jenner took matter from a cowpox pustule on milkmaid Sarah Nelmes and inoculated eight-year-old James Phipps. The boy developed a mild fever but recovered. Jenner then exposed Phipps to smallpox matter on multiple occasions; the boy showed no ill effects. Jenner published his findings in 1798 in a work titled An Inquiry into the Causes and Effects of the Variolae Vaccinae.
The procedure Jenner developed was named vaccination, from the Latin vacca meaning cow. It was safer than inoculation because it used a different, milder disease rather than smallpox itself. Jenner did not fully understand why it worked — germ theory and the concept of antibodies lay decades ahead — but he had shown through careful observation and testing that it did.
Spreading Vaccination: Resistance and Compulsion
Vaccination spread unevenly. Many doctors were sceptical; the medical establishment initially resisted Jenner’s claims. Religious opposition also emerged — some people objected to using animal material. Satirical cartoonists depicted vaccinated people growing horns and bovine features. Acceptance grew as evidence mounted. In 1840, inoculation was made illegal in Britain and vaccination against smallpox was offered free. In 1853, smallpox vaccination was made compulsory for all infants. In 1867, this was extended and fines introduced for non-compliance. Despite anti-vaccination protests, compulsory vaccination substantially reduced smallpox deaths in Britain.
Jenner used cowpox matter to vaccinate James Phipps in 1796, demonstrating protection against smallpox. Vaccination became compulsory for infants in 1853. Smallpox was eventually eradicated globally in 1980, the only human disease ever to be eliminated entirely.
The scientific explanation for why vaccination worked only came after germ theory had been established. In 1890, German scientists Emil von Behring and Shibasaburo Kitasato demonstrated that the blood of animals exposed to weakened diphtheria toxin contained substances that neutralised the toxin — the first identification of what we now call antibodies. This discovery won von Behring the first Nobel Prize in Physiology or Medicine in 1901. Understanding antibodies allowed scientists to develop increasingly targeted vaccines and, later, therapeutic anti-sera. It transformed the scientific basis of disease prevention from empirical observation to mechanistic understanding.
Change and Continuity in Disease Prevention
Looking across the period from 1500 to the present, the most significant change in disease prevention is the move from prayer and purification to scientifically validated immunisation programmes. Yet elements of continuity persist: quarantine — used against plague in 1348 — was still used during the COVID-19 pandemic in 2020. Hesitancy about vaccination, recorded since Jenner’s time, remains a challenge for public health today. The factors that drove change included scientific progress (germ theory, bacteriology), government action (compulsory vaccination acts, public health legislation) and improvements in education and communication.