Smallpox

Résumé fourni par la source

You have erased from the calendar of human afflictions one of its greatest. Yours is the comfortable reflection that mankind can never forget that you have lived. Future nations will know by history only that the loathsome smallpox has existed and by you has been extirpated. Thomas Jefferson, writing to Edward Jenner in 1806 [1]. Before knowledge and use of vaccines, protection against smallpox was practiced more than a thousand years ago by traditional approaches. Invoking the good graces of smallpox gods, goddesses, and saints by individuals and communities was common [2]. Isolation of patients was the only means known to appease and contain the bad spirits that brought and spread the disease. Traditional medical practitioners in some areas of China, India, Egypt, Ethiopia, and elsewhere collected materials from the pustules or crusts of the afflicted and inserted these into the noses or skin of healthy persons seeking protection [2]. This procedure, called inoculation or variolation, probably had little effect on curtailing epidemics because of its limited use and variability of potency of the inoculum. It is remarkable that some early inoculators inserted scabs into the nose, without understanding that smallpox is acquired via the respiratory route, and, that scratching pustular material into the skin could have the same salutary effect. Nasal inoculation or dermal variolation, using material containing live virus, resulted sometimes in mild illness and protection. However, some cases of smallpox in recipients had the potential to spread within persons and communities. Edward Jenner, the country doctor from Berkeley, Gloucester, England, is recognized as the father of smallpox vaccination. Jenner’s 1796 observations, that cowpox protected against smallpox when scratched into the skin of recipients, were written up in detail and presented to the Royal Society of England in 1798 and promoted widely in letters [3]. Yet Jenner was not the first to make these observations. Some historians note that John Fewster and others, as early as 1768, living near Jenner in Thornbury, and Benjamin Jesty in 1774 in Westminster, United Kingdom, observed the benefits of cowpox inoculation for protecting humans against smallpox [4]; these observations were not documented and disseminated, however, so they remain in obscurity. Jenner promoted vaccines in England and elsewhere by letters and speeches and by giving vaccinations gratis to local residents at the “vaccine hut” outside his home (The Chantry). There was immediate fierce opposition by persons who believed that biological products from cows would result in growths resembling cows on the bodies of recipients. People of influence had an early role in supporting both inoculation and vaccination. Lady Mary Wortley Montagu, wife of the UK Ambassador to Turkey, who had had smallpox in England, observed variolators in Turkey performing inoculations. She was so impressed that she promoted the procedure via a series of letters starting in 1717 [1, 2]. Thomas Jefferson, Benjamin Franklin, and Benjamin Waterhouse, the latter of Harvard University, were early advocates of vaccination in the United States. For the next 100 years, technical problems tied to vaccine quality impeded the successful use of vaccine globally. Well into the 20th century, the major challenges were growing adequate quantities of vaccine of measurable potency, sterility, and durability despite differences in temperature, climate, and humidity [5]. Mode of administration was another challenge. Different scratch and inoculation techniques were used, particularly in India [6]. Throughout much of the 1800s vaccine was passed from arm to arm or dried and put on small “points” (sharp objects of ivory, steel). These methods were not reliable. Toward the end of the 19th century, animals, especially the skin of living cows, were used to grow the virus used for vaccination [5]. During the 19th century, arm-to-arm vaccination was the standard method of maintaining the product’s efficacy, even during long voyages. Some practitioners put threads through the pustular material. The threads were dried and sent to the areas for populations to be vaccinated; potency certainly waned during such travel. On long sea voyages, groups of orphan children were often sent specifically to assure arm-to-arm transfer of the pustular material. In the early 1900s, an attempt to dry and preserve vaccine for shipment from France to their colonies in West Africa was described by Fasquelle and Fasquelle [7]. Pustular material from cows or patients with pustular disease of indeterminate origin was used for more than a century as the source of smallpox vaccine. By the beginning of the 1900s, vaccination against smallpox was being practiced in most industrialized countries. The virus now used, called vaccinia, has an obscure origin. The product may have originally been a hybrid between cowpox virus and variola virus or some other orthopoxvirus by serial passage in artificial conditions, or, as Baxby posits, vaccinia may be a laboratory survivor of a virus now extinct [8], p 214]. The various vaccinia strains globally are similar to each other genetically but differentiated from other poxviruses, including cowpox and variola viruses, by DNA mapping. By the 1950s there was improvement in vaccine quality, distribution, and public health infrastructure. Smallpox was virtually eliminated from Europe and North America by that time. Since Jenner’s time opponents of vaccination have based their concerns on perceived physical harm from the procedure and breaching of individual rights. Over time, vaccination has been considered a public health good and inserted into law in the United States and elsewhere and upheld by the Supreme Court [9]. High vaccination coverage had been the strategy of national and international smallpox control and elimination strategies since Jenner’s findings slowly spread worldwide and became accepted in the 1800s. However, the continued existence of the disease on virtually all continents was due to fragmented and inadequate health systems. Access to remote populations was impossible in many areas and acceptance of evolving vaccine production and delivery technology was slow. Most importantly, the colonial legacy starting in the late 1800s left many areas of the world dependent on European control and resources for their health and other programs, particularly in Africa. Conservation of liquid vaccine produced mainly on cows was very difficult, because refrigeration was virtually nonexistent in the tropics until the mid- to late-1900s. In West and Central Africa and India more vaccinations were given than the censused population, yet smallpox raged because of poor vaccine quality. Massive epidemics of smallpox appeared periodically in virtually all tropical countries and several areas of temperate countries well into the 1900s, fueled by high levels of susceptibility as a result of new births, those who received poor quality vaccine, and nonimmune older persons [10]. The World Health Organization (WHO) was formed in 1948 with a mandate to develop public health policies and to coordinate surveillance, and some control and eradication initiatives. By the 1950s, many countries had passed public health laws and implemented smallpox vaccination programs, many of which were successful, particularly in the northern hemisphere. In 1959, the representative of the Soviet Union proposed a resolution for a global smallpox eradication program to the World Health Assembly [2]; this was based, in part, on the outbreaks of smallpox in several of the southern republics, which underscored the priority for development of a potent vaccine to control the outbreaks. In addition, the Soviets wished to provide vaccines to the WHO as a gift to the global program. Yet, little progress was made over the next 6 years toward global eradication [11], p 334]. Between 1959 and 1966, few funds were rec