Each one of us is constantly warding off the potential for infection or disease. After all, the world is filled with countless microbes, fortunately most of which are harmless and some even beneficial. But there are plenty of microbes that can hurt us (pathogens, from the Greek word for disease, “pathos”). Harmful bacteria, for example, may cause disease through infection of their host or by the release of powerful toxins. Viruses, inert by themselves, have the ability to invade the cells of other life forms. As those cells duplicate, so does the virus. While one’s ability to ward off disease is usually strong, there are instances where the microbes overwhelm the body and produce illness. In an effort to protect against many infectious diseases, we rely on vaccines with the intent of conferring protection and immunity.

Vaccines have been a vehicle for disease prevention and eradication for hundreds of years. The development and widespread distribution of safe, effective, and affordable vaccines has done more for disease prevention over time than nearly any other medical or public health intervention. Of the 10 greatest public health achievements over time, certainly immunization against disease ranks at or near the top of the list.[2] Millions of lives have been saved because of the widespread use of vaccines to prevent or eradicate diseases such as measles, diphtheria, pertussis, tetanus, polio, and, of course, smallpox. The eradication of smallpox worldwide is undoubtedly one of the most spectacular public health initiatives of all time.

Vaccination not only protects an individual from disease, but also has the dual role of protecting the community at large from disease outbreaks.

For disease to spread, there must be a pool of susceptible people in whom the bacteria or virus can grow. Ironically, those who elect not to vaccinate themselves or their children are actually benefiting from those who are vaccinated. This concept is referred to as “herd immunity.” When a disease spreads from one human to another, it requires both an infected person to spread it and a susceptible person to catch it. Herd immunity works by decreasing the number of susceptible individuals, even those who refuse to be vaccinated, and when this number drops low enough, the disease will disappear from the community because there are not enough people to continue the catch-and-infect cycle. The greater the proportion of vaccinated individuals, the more rapidly the disease will disappear. Once-common diseases such as pertussis, polio, smallpox, and measles have all but disappeared thanks to the large numbers of individuals who are vaccinated against these diseases. Periodically, however, there have been mini-outbreaks of disease for which there are vaccinations. For example, there are outbreaks of measles (a particularly contagious, potentially serious disease) in the United States as well as around the world, primarily as a result of a pool of unvaccinated children.
Those who are not vaccinated are at high risk of contracting this disease.[3]

Because microbes know no foreign boundary, diseases in one part of the world can quickly and easily spread to other parts of the globe. As such, a unified global vaccination policy is needed; how to achieve such a noble and important goal, however, often is not easily accomplished. Economics, politics, and social constraints can and do play important roles in disease-eradication programs. The success of immunization policies depends on, and is linked with, interrelated factors, including vaccine safety (quality control and monitoring), adequate vaccine supply (to avoid vaccine shortages), effective delivery systems to ensure that the vaccines get to those in need (more of an issue in the developing world), financial incentives and legal protection for the vaccine manufacturers, and educational efforts to inform the public about the benefits and risks of vaccinations. Indeed, perhaps most of all, there is a need to focus on the public’s fears about the safety of vaccination and their willingness to be immunized.

In addition to the scientific challenges to vaccine development, social, ethical, economic, legal, and political issues individually and collectively have served to curtail and in some cases to derail efforts to immunize populations. Vociferous antivaccination movements frequently clashed with the government’s authority to immunize for the “common good.” Historically, antivaccinationists have protested against what they consider the intrusion of their privacy and bodily integrity. One of the potent symbols of the early antivaccine movement was the limp “Raggedy Ann” doll, which was created in 1915 by a man whose daughter died shortly after being vaccinated in school without parental consent.  The medical authorities blamed a heart defect, but the parents blamed their child’s death on the shot. Since that time, there have been reports of deep-seated public fears of vaccinations, as well as protests against compulsory vaccination laws.

The issue of vaccine safety periodically makes front-page news, usually after an unfortunate event in which someone or many individuals were harmed in some way allegedly as a result of being vaccinated. Proponents of vaccination would be the last to say that vaccination is risk free, but they would be the first to argue that the small risks outweigh the dangers of not being vaccinated. To lose ground to the tremendous achievements realized by vaccines because of the public’s mistrust could be potentially serious. Are the antivaccinationists off base, or are their concerns valid? How should the public health and medical communities respond? What role should government have to legally enforce vaccination policy? This chapter focuses on the history of vaccines and immunization and the new challenges that must be addressed to ensure against a resurgence in vaccine-preventable diseases locally, nationally, and globally.

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Tony Rosen, MPH, MD
Tony Rosen, Division of Geriatric Medicine and Gerontology, Weill Cornell Medical College, Cornell University, New York, New York;

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REFERENCES

1. Barquest N, Domingo P. Smallpox: the triumph over the most terrible of the ministers of death. Ann Internal Med. 1997;127:627.
2. US Centers for Disease Control and Prevention. Ten great public health achievements in the twentieth century, 1900-1999.
3.   Parker AA. Implications of a 2005 measles outbreak in Indiana for sustained elimination of measles in the United States. New Engl J Med. 2006;355:1184.
4. Okonek BAM, Peters PM. Vaccines: how and why
5. Baxby D. Vaccination: Jenner’s Legacy. Berkeley, UK: Jenner Educational Trust; 1994. 6. Parish HJ. A History of Immunization. Edinburgh, UK: Livingstone; 1965.
6. Gross CP, Sepkowitz K. The myth of the medical breakthrough: smallpox, vaccination, and Jenner reconsidered. Int J Infect Dis. 1998;3:54-60.
7. Salmon DA,  et al.  Compulsory vaccination and conscientious or philosophical exemptions: past, present, and future. Lancet. 2006;367(9508):436-442.

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