Article: Vaccination

Vaccination is the process of administering weakened or dead pathogens to a healthy person, with the intent of conferring immunity against a targeted form of a related disease agent.

The term was coined by Edward Jenner and adapted by Louis Pasteur for his pioneering work in vaccination. Vaccination (Latin: vacca—cow) is so named because the first vaccine was derived from a virus affecting cows: the cowpox virus, a relatively benign virus that provides a degree of immunity to smallpox, a contagious and deadly disease. In common speech, 'vaccination' and 'immunization' generally have the same colloquial meaning. Vaccination efforts were initially met with some resistance before early success brought widespread acceptance and mass vaccination campaigns were undertaken.

The eradication of smallpox, which was last seen in a natural case in 1977, is considered the most spectacular success of vaccination. Some people assert that childhood vaccination plays a role in autoimmune disease and autism, though large-scale scientific studies have not shown any link.

Triggering immune sensitization

In the generic sense, the process of artificial induction of immunity, in an effort to protect against infectious disease, works by 'priming' the immune system with an 'immunogen'. Stimulating immune response, via use of an infectious agent, is known as immunization. Vaccinations involve the administration of one or more immunogens, in the form of live, but weakened (attenuated) infectious agents, which normally are either weaker, but closely-related species (as with smallpox and cowpox), or strains weakened by some process. In such cases, an immunogen is called a vaccine.

Some modern vaccines are administered after the patient already has contracted a disease, as in the cases of experimental AIDS, cancer and Alzheimer's disease vaccines. Vaccinia given after exposure to smallpox, within the first four days, is reported to attenuate the disease considerably, and vaccination within the first week is known to be beneficial to a degree. The first Rabies immunisation was given by Pasteur to a child bitten by a rabid dog, and then and subsequently post-exposure immunisation to Rabies has generally been followed by survival. The essential empiricism behind such immunizations is that the vaccine triggers an immune response more rapidly than the natural infection itself.

Most vaccines are given by hypodermic injection as they are not absorbed reliably through the gut. Live attenuated Polio, some Typhoid and Cholera Vaccines are given orally in order to produce immunity based in the bowel.

History of vaccinations

Vaccination campaigns have spread throughout the globe since Jenner's smallpox vaccine of 1796, sometimes prescribed by law or regulations (See vaccination Acts). Vaccines are now used to fight a wide variety of disease threats besides smallpox. Louis Pasteur further developed the technique during the 19th century, extending its use to protecting against bacterial anthrax and viral rabies. The method Pasteur used entailed treating the infectious agents for those diseases so they lost the ability to cause serious disease. Pasteur adopted the name vaccine as a generic term in honor of Jenner's discovery, which Pasteur's work built upon.

Prior to vaccination with cowpox, the only known protection against smallpox was inoculation or variolation (Variola - the Smallpox viruses) where a small amount of live smallpox virus was administered to the patient; this carried the serious risk that the patient would be killed or seriously ill. The death rate from variolation was reported to be around a tenth of that from natural infection with Variola, and the immunity provided was considered quite reliable. Factors contributing to the efficacy of variolation probably include the choices of Variola Minor strains used, the relatively low number of cells infected in the first phase of multiplication following initial exposure, and the exposure route used, via the skin or nasal lining rather than inhalation of droplets into the lungs.

Consistency would suggest the activity should have predated Jenner's description of an effective vaccination system, and there is some history relating to opposition to the older and more hazardous procedure of variolation.

In modern times, the first vaccine-preventible disease targeted for eradication was smallpox. The World Health Organization coordinated the global effort to eradicate this disease. The last naturally occurring case of smallpox occurred in Somalia in 1977.

In 1988, the governing body of W.H.O. targeted polio for eradication by the year 2000. Although the target was missed, eradication is very close. The next eradication target would most likely be measles, which has declined since the introduction of measles vaccination in 1963.

In 2000, the Global Alliance for Vaccines and Immunization was established to strengthen routine vaccinations and introduce new and under-used vaccines in countries with a per capita GDP of under US$1000. GAVI is now entering its second phase of funding, which extends through 2014.

Compulsory vaccination and opposition to vaccination

In an attempt to eliminate the risk of outbreaks of some diseases, several governments and other institutions have instituted policies requiring vaccination for all people. For example, an 1853 law required universal vaccination against smallpox in England and Wales, with fines levied on people who did not comply. In the United States, the Supreme Court ruled in the 1905 case Jacobson v. Commonwealth of Massachusetts that the state could require individuals to be vaccinated for the common good. Common contemporary vaccination policies require that children receive common vaccinations before entering school. Compulsory vaccination is believed to have greatly reduced the rates of some infectious diseases.^[1]

Beginning with early vaccination in the nineteenth century, these policies led to resistance from a variety of groups, collectively called anti-vaccinationists, who objected on ethical, political, medical safety, religious, and other grounds. Common objections are that compulsory vaccination represents excessive government intervention in personal matters, or that the proposed vaccinations are not sufficiently safe. Many modern vaccination policies allow exemptions for people who have compromised immune systems, allergies to the components used in vaccinations or strongly-held objections.^[1]

Herd immunity and medical risk management issues

Vaccination campaigns are generally accepted as having contributed to the worldwide elimination of smallpox, through herd immunity, and to the restriction of polio to isolated pockets in countries where healthcare access is difficult. The risk management practices of government health agencies' promoting widespread vaccination campaigns has prompted increasing controversy in recent years, despite the fact that many once-common childhood diseases, such as mumps, measles and rubella, are now relatively rare in developed countries.

Nevertheless, vaccination campaigns may have unfortunate co-evolutionary side-effects, particularly if they produce a selective pressure in favor of certain strains against which there are no vaccines or treatment. Another problem related to co-evolution is that vaccines that may eliminate one infectious diseases or another may, in turn, allow others to thrive in the ecological niche that has been vacated. For example, it has been postulated that (the less-often-fatal) serogroup-B meningitis strains may expand into the niche provided if serogroup-C is largely eradicated through vaccination. However, while there has been a rise in serogroup-B meningitis, there is as yet no evidence to link this to the meningitis-C vaccination.

An incompletely-successful attempt at eradication of a disease through vaccination might increase the average age of contraction of the disease. In diseases such as measles, where there is a higher rate of complication in older people, the overall effect might, in theory, be to cause more deaths than before the vaccination was introduced. Potentially, this could be a 'perverse effect' of vaccination campaigns. Observation of immunity levels in a population over many years has been followed by booster immunization programs, for instance, in the United Kingdom, with measles and mumps.

Adjuvants and preservatives

Vaccines typically contain one or more adjuvants, used to boost the immune response. Tetanus toxoid for instance is usually adsorbed onto Alum. This presents the antigen in such a way as to produce a greater action than the simple aqueous tetanus toxoid. People who get an excessive reaction to adsorbed tetanus toxoid may be given the simple vaccine when time for a booster occurs.

In the preparation for the 1990 Gulf campaign, Pertussis vaccine (not acellular) was used as an adjuvant for Anthrax vaccine. This produces a more rapid immune response than giving only the Anthrax, which is of some benefit if exposure might be imminent.

They may also contain preservatives, which are used to prevent contamination with bacteria or fungi. Until recent years, the preservative thimerosal was used in many vaccines that did not contain live virus. As of 2005, the only childhood vaccine in the U.S.A. that contains thiomerosal is the influenza vaccine [1], which is currently recommended only for children with certain risk factors.^[2] The UK is considering Influenza immunisation in children perhaps as soon as in 2006-7. Single-dose Influenza vaccines supplied in the UK do not list Thiomersal (its UK name) in the ingredients. Preservatives may be used at various stages of production of vaccines, and the most sophisticated methods of measurement might detect traces of them in the finished product, as they may in the environment and population as a whole[2].

Vaccine research

Some major contemporary research in vaccination focuses on development of vaccinations for diseases including HIV and malaria.

Vaccine is an international peer-reviewed journal for vaccination researchers, indexed in Medline pISSN: 0264-410X.

See also

• Vaccine controversy