inoculation, in medicine, introduction of a preparation into the tissues or fluids of the body for the purpose of preventing or curing certain diseases. The preparation is usually a weakened culture of the agent causing the disease, as in vaccination against smallpox; however, it may also be composed of antitoxins, which provide immunity themselves, or toxoids, which are proteins that stimulate the body to produce antitoxins (see immunity). Various forms of inoculation were used from ancient times in China, India, and Persia, but it remained for the English physician Edward Jenner in the late 18th cent. to demonstrate its feasibility to the Western world. The term inoculation is used also to refer to the introduction of certain substances into plant tissues or to the placement of microorganisms into culture media (for experimental or diagnostic purposes) or into the soil.
Inoculation is the placement of something to where it will grow or reproduce, and is most commonly used in respect of the introduction of a serum, vaccine, or antigenic substance into the body of a human or animal, especially to produce or boost immunity to a specific disease; but also can be used to refer to the communication of a disease to a living organism by transferring its causative agent into the organism, to implant microorganisms or infectious material into a culture medium such as a brewers vat or a petri dish, to safeguard as if by inoculation, to introduce an idea or attitude into someone's mind, any placement of microorganisms or viruses at a site where infection is possible such as to increase soybeans' nitrogen fixation one can treat soybeans at planting with Rhizobium japonicum inoculant. The verb "to inoculate" is from Middle English "inoculaten", which meant "to graft a scion (a scion is a plant part to be grafted onto another plant); which in turn is from Latin "inoculare", past participle "inoculat-".

This article covers variolation, inoculation as a method of purposefully infecting a person with smallpox (Variola) in a controlled manner so as to minimise the severity of the infection and also to induce immunity against further infection. See vaccination for post-variolation methods of safeguarding as if by inoculation by administering weakened or dead pathogens to a healthy person or animal with the intent of conferring immunity against a targeted form of a related disease agent.

Today the terms inoculation, vaccination and immunisation are used more or less interchangeably and popularly refer to the process of artificial induction of immunity against various infectious diseases. The microorganism used in an inoculation is called the inoculant or inoculum.



The earliest record of inoculation is thought to be found in 8th century India, when Madhav wrote the Nidāna, a 79-chapter book which lists diseases along with their causes, symptoms, and complications. According to Donald R. Hopkins (2002), Madhav included a special chapter on smallpox (masūrikā) and described the method of inoculation to protect against smallpox. Dominik Wujastyk (1995), however, argues that inoculation is not mentioned in any ancient Sanskrit medical treatises and that it was a rumor which began in the 19th century:

Inoculation was current in Turkey in the early eighteenth century; there is evidence that it may have been brought to Turkey from China. It is interesting, then, to find a detailed account by a renowned English surgeon in 1767, describing the widespread practice of inoculation in Bengal. There is also some evidence to push the Indian practice of inoculation back further, to 1731. Once again, there is a historical paradox here: there is not the slightest trace of this important and effective treatment in any of the Sanskrit medical treatises. Smallpox was certainly recognised in Ayurvedic texts, where it is called masurika ('lentil' disease) and was treated after a fashion. But of inoculation there is absolutely no mention. The link between theory and practice is broken once again.

After smallpox vaccination was introduced to India in 1802, a rumour was started in 1819 by an article in The Madras Courier, a popular daily newspaper, to the effect that there existed in ancient Sanskrit text describing in detail the process of vaccination. This proved, it was argued, the superiority of ancient Indian science, and that 'there is nothing new under the sun'. Unfortunately, this rumour gained currency and was republished in books and encyclopedias across Europe all through the nineteenth century, and it even surfaces today. Careful literary research has shown, however, that no such Sanskrit text exists, and that the whole affair was almost certainly triggered by the excessive zeal of British vaccination propagandists, who composed tracts on vaccination in local languages and probably in Sanskrit too.


Robert Temple writes that the practice of inoculation for smallpox began in China during the 10th century. A Song Dynasty (960–1279) chancellor of China, Wang Dan (957–1017), lost his eldest son to smallpox and sought a means to spare the rest of his family from the disease, so he summoned physicians, wise men, and magicians from all across the empire to convene at the capital in Kaifeng and share ideas on how to cure patients of it. From Mount Emei in Sichuan, a Daoist hermit, a nun known as a "numinous old woman" and "holy physician"—who Temple says was associated with the 'school of the ancient immortals' and thus most likely specialized in 'internal alchemy'—introduced the technique of inoculation to the capital. However, Joseph Needham states that this information comes from the Zhongdou xinfa (種痘心法) written in 1808 by Zhu Yiliang, centuries after the alleged events.

The first clear and credible reference to smallpox inoculation in China comes from Wan Quan's (1499–1582) Douzhen xinfa (痘疹心法) of 1549, which states that some women unexpectedly menstruate during the procedure, yet his text did not give details on techniques of inoculation. Inoculation was first vividly described by Yu Chang in his book Yuyi cao (寓意草), or Notes on My Judgment, published in 1643. Inoculation was reportedly not widely practiced in China until the reign of the Longqing Emperor (r. 1567–1572) during the Ming Dynasty (1368–1644), as written by Yu Tianchi in his Shadou jijie (痧痘集解) of 1727, which he alleges was based on Wang Zhangren's Douzhen jinjing lu (痘疹金鏡錄) of 1579. From these accounts, it is known that the Chinese banned the practice of using smallpox material from patients who actually had the full-blown disease of Variola major (considered too dangerous); instead they used proxy material of a cotton plug inserted into the nose of a person who had already been inoculated and had only a few scabs, i.e. Variola minor. This was called "to implant the sprouts", an idea of transplanting the disease which fit their conception of beansprouts in germination. Robert Temple quotes an account from Zhang Yan's Zhongdou xinshu (種痘新書), or New book on smallpox inoculation, written in 1741 during the Qing Dynasty (1644–1912), which shows how the Chinese process had become refined up until that point:

Method of storing the material. Wrap the scabs carefully in paper and put them into a small container bottle. Cork it tightly so that the activity is not dissipated. The container must not be exposed to sunlight or warmed beside a fire. It is best to carry it for some time on the person so that the scabs dry naturally and slowly. The container should be marked clearly with the date on which the contents were taken from the patient.

In winter, the material has yang potency within it, so it remains active even after being kept from thirty to forty days. But in summer the yang potency will be lost in approximately twenty days. The best material is that which had not been left too long, for when the yang potency is abundant it will give a 'take' with nine persons out of ten people—and finally it becomes completely inactive, and will not work at all. In situations where new scabs are rare and the requirement great, it is possible to mix new scabs with the more aged ones, but in this case more of the powder should be blown into the nostril when the inoculation is done.

As for other methods used in China, the technique of scratching the skin and putting pox onto the scab seems to have developed later than the first accounts made in China, and possibly came from Central Asia—according to Temple.

Importation to the West

The practice was introduced to the west by Lady Mary Wortley Montagu (May 26, 1689-August 21, 1762). Lady Montagu's husband, Edward Wortley Montagu, served as the British ambassador to the Ottoman Empire from 1716 to 1717. She witnessed inoculation being practiced by physicians in Constantinople, and was greatly impressed: she had lost a brother to smallpox and bore facial scars from the disease herself. In March 1718 she had the embassy surgeon, Charles Maitland, inoculate her five-year-old son. In 1721, after returning to England, she had her four-year-old daughter inoculated. She invited friends to see her daughter, including Sir Hans Sloane, the King's physician. Sufficient interest arose that Maitland gained permission to test inoculation at Newgate prison in exchange for their freedom on six prisoners due to be hanged, an experiment which was witnessed by a number of notable doctors. All survived, and in 1722 the Prince of Wales' daughters received inoculations.

The practice of inoculation slowly spread amongst the royal families of Europe, usually followed by more general adoption amongst the people.

The practice is documented in America as early as 1721, when Zabdiel Boylston, at the urging of Cotton Mather, successfully inoculated two slaves and his own son. Mather, a prominent Boston minister, had heard a description of the African practice of inoculation from his Sudanese slave, Onesimus, in 1706, but had been previously unable to convince local physicians to attempt the procedure. Following this initial success, Boylston began performing inoculations throughout Boston, despite much controversy and at least one attempt upon his life. The effectiveness of the procedure was proven when, of the nearly three hundred people Boylston inoculated during the outbreak, only six died, whereas the mortality rate among those who contracted the disease naturally was one in six.

Natural experiment in inoculation
around Boston, 1721
  Total Died % Mortality
Variolated c 300 6 c 2%
Unvariolated c 6000 c 1000 "about 14%"

In France considerable opposition arose to the introduction of inoculation. Voltaire, in his Lettres Philosophiques, wrote a criticism of his countrymen for being opposed to inoculation and having so little regard for the welfare of their children, concluding that "had inoculation been practised in France it would have saved the lives of thousands.".

Inoculation grew in popularity in Europe through the 18th century. Given the high prevalence and often severe consequences of smallpox in Europe in the 18th century (according to Voltaire, there was a 60% incidence of first infection, a 20% mortality rate, and a 20% incidence of severe scarring), many parents felt that the benefits of inoculation outweighted the risks and so inoculated their children.


Two forms of the disease of Smallpox were recognised, now known to be due to two strains of the Variola virus. Those contracting Variola Minor had a greatly reduced risk of death — 1-2% — compared to those contracting Variola Major with 20% mortality. Infection via inhaled viral particles in droplets spread the infection more widely than the deliberate infection through a small skin wound. The smaller, localised infection is adequate to stimulate the immune system to produce specific immunity to the virus, while requiring more generations of the virus to reach levels of infection likely to kill the patient. The rising immunity terminates the infection. So the twofold effect is to ensure the less fatal form of the disease is the one caught, and to give the immune system the best start possible in combating it.

Inoculation in the East was historically performed by blowing smallpox crusts into the nostril. In Britain, Europe and the American Colonies the preferred method was rubbing material from a smallpox pustule from a selected mild case (Variola minor) into a scratch between the thumb and forefinger. This would generally be performed when an individual was in normal good health, and thus at peak resistance. The recipient would develop smallpox; however, due to being introduced through the skin rather than the lungs, and possibly because of the inoculated individual's preexisting state of good health, the small inoculum, and the single point of initial infection, the resulting case of smallpox was generally milder than the naturally-occurring form, produced far less facial scarring, and had a far lower mortality rate. As with survivors of the natural disease, the inoculated individual was subsequently immune to re-infection.

Supplanted by vaccination

In 1796, Edward Jenner introduced the far safer method of inoculation with the cowpox virus, a non-fatal virus that also induced immunity to smallpox. This led to smallpox inoculation falling into disuse and eventually being banned in England in 1840.

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