Virus and Vaccination
The smallpox virus (variola), which reproduces by essentially hijacking the mitochondrial DNA of the cells of a human host and using it to replicate, has been entrenched in high-density human populations since the 12th century BCE. It was endemic (i.e. could be found in the native populations) in North Africa, Asia, Europe, and the Mediterranean coastal areas throughout recorded history. Persons from this genetic heritage did not acquire immunity, as is often believed, since the immunity of a person who has survived smallpox is not passed on to offspring. The virus thus had a constant supply of human hosts through the generations.
The factors that can cause this ever- present threat to manifest as an epidemic are manifold, chiefly population density (hence the term "crowd diseases" for this and other highly contagious diseases) and a lack of experience in strategies of treatment, quarantine, and containment of the infected hosts and hence the disease carriers. In the case of smallpox, controlling the disease carrier is synonymous with treatment of the victims, since the virus only affects humans, and does not survive long outside the human host. The virus is most easily spread on the vapour droplets of the breath (i.e. sneezing), which is inhaled by other persons who find themselves in close proximity to the infected person. The antique term "effluvia" was commonly used to describe the vapours, smells, and other intangible excrecences of a body, and was probably the concept through which the spread of smallpox was understood before the revelations of late 18th century microbiological investigations. The virus is also present in effective concentrations in the scabrous material that forms on, and then is shed from, the lesions on the body in the last stages of the disease. In the 6th century, Chinese physicians had already recognised this and used the powdered scabs as the basis for rudimentary inoculation.
Inoculation is the theory and practice of exposing a healthy person to a reduced concentration or a weaker strain of the virus, typically through broken skin, with the expectation that the persons immune system will successfully fight the disease and thus develop a lifelong immunity to even the most potent concentrations of the virus. Inoculation (originally called variolation) was sometimes done by striking the skin of a victim who had a mild outbreak of smallpox with a prickly branch, and transferring small amounts of the infectious material to a recipient by striking their bare skin with the same branch. These inoculations were often carried out in "pox houses" where victims of the disease were quarantined, and samples of infectious material were sold for the purposes of immunization (inoculation or variolation). In some countries, notably India, people in the past sought to acquire immunity by sleeping next to an infected person or by wearing their clothes. The first recorded use of inoculation by western Europeans occurred in 1717; the recipient was the six-year old son of a English ambassador to Constantinople.1 Inoculation results, ideally, in the recipient manifesting minor symptoms of the disease, with resulting immunity to further exposure. The risks of contracting full-blown smallpox through inoculation were considerable; one source cites 1 of 500 recipients dying as a result.2
It had long been noticed that in rural farming communities the milk-maids were frequently free of the scarring left by smallpox on survivors. In the late 18th century it was discovered that persons who had contracted the non-lethal cowpox (variolae vaccinae) from infected dairy animals were usually immune to smallpox. Cowpox symptoms manifest in humans as mild fevers, with pustules erupting on the hands that heal without the characteristic scarring of smallpox. Between 1796 and 1798, British physician Edward Jenner used bovine serum containing the cowpox virus to successfully inoculate patients against smallpox. The cowpox virus is genetically related to the smallpox virus and though not fatal to humans, causes the body to produce antigens that protect the recipient from infection by smallpox. This preventative treatment was called vaccination after vacca, the Latin word for cow.
The term vaccination was later used for all types of immunization, hence the frequent confusion between the terms vaccination and inoculation. Vaccination against smallpox became mandatory in England in 1834 and was the only form of preventative treatment for smallpox permitted by the British Government after 1840.3 Neither vaccination not inoculation were 100% effective, since the process by which the body's immune system forms a lifelong protection against the illness was not clearly understood in the 19th century. The preventative treatments were often applied by inexpert practitioners, leading to failure of the vaccination to protect the recipient. In the case of inoculation with the actual smallpox virus, the result was frequently fatal, leading to enormous controversy regarding the efficacy, ethics, and practice of vaccination. Factions both for and opposed to the preventative treatment published treatises and propaganda that were hotly debated in medical, churchly, and public circles until the early 20th century.