Difference between revisions of "Vaccine"

Revision as of 03:54, January 22, 2008

Avian flu vaccine development

A vaccine is an injection of a specialized protein designed to create an immunity to a particular disease (see antigen). The primary mechanism that a body uses to identify infections is a protein molecule called an antibody. The ingredients of vaccines used today are available from the CDC.^[1]

Traditionally a few highly tested vaccines were mandatory for children to protect against deadly or severe diseases, such as smallpox and polio. In the 1990s, vaccine manufacturers began introducing and persuading states to require numerous additional vaccines for non-deadly and even sexually transmitted diseases. About one-third of the states have philosophical exemptions entitling parents to decline the vaccines; 48 out of 50 states have religious exemptions; all states have medical exemptions, but they are hardest to obtain.^[2][3]

If the body has a particular antibody for a particular disease it can identify the infection early on and the immune system can destroy it. Vaccines work by exposing the body to a form of the disease in such a way that it will not cause illness but allow antibodies to develop. This confers a level of immunity to the organism vaccinated.^[4]

There are four major types of vaccines and they are differentiated by what antigen is used. Live attenuated vaccines are created from the actual disease in question, however before injection the pathogen is attenuated (weakened) by growing successive generations of lines in poor nutrient conditions. It is possible for these vaccines to still cause an infection. Inactivated vaccines are created from pathogens that have been killed, usually with the use of a preservative formaldehyde. Toxoid vaccines are created by using toxins produced by the pathogen, before injection these toxins are exposed to heat and chemicals that eliminate their effect, antibodies will still be produced to these deactivated toxins. Finally, component vaccines use pieces of the pathogen in the injection. These pieces often of identifying protein segments that allow antibodies to be produced.^[5]

Only live attenuated vaccines can still cause infection.The other three types of vaccines can cause illness, but this is an allergic response not due to the disease itself. Very rarely a serious disease known as eczema vaccinatum can emerge. Vaccines that use pieces of pathogens often use a carrier virus in the injection. Those with very weak immune systems that are exposed to such a vaccine can become infected with the carrier virus and develop eczema. A recent case of this was reported in the United States after a military man was vaccinated with small pox and his two year old son became ill. ^[6]

Since the adoption of vaccination, however, many diseases have been curbed. Smallpox, a deadly disease responsible for the deaths of millions, has been mostly eliminated through vaccination. Responsible for an estimated 300 to 500 million deaths worldwide in the 20th century, effective vaccination programs of the 19th and 20th century were effective at curbing the disease, and in 1979 the World Health Organization declared smallpox to be eradicated.

Polio, for example, killed over 3,000 people in the United States in 1952 [1], and inflicted such noted persons as President Franklin Delano Roosevelt, actor Alan Alda, and musician Itzak Perlman. When doctors began using a vaccine to fight polio, it practically eradicated the disease in the developed world.

Other diseases that have been curbed since the invention of vaccines include measles, mumps, rubella, and typhoid.

Influenza Vaccine

The flu vaccine is an example of modern vaccination. Due to the change in allele frequency over time in the population of the influenza virus, new influenza vaccines are created each year. According to the CDC ^[7],

Influenza viruses are always changing. Therefore, influenza vaccines are updated every year, and an annual vaccination is recommended.

Since production of the vaccine must begin many months before the influenza season starts models of the population genetics of the virus must be produced. ^[8] The success of vaccinations programs is dependent on the accuracy of these predictions.^[9] The National Institute of Health recently assigned $26 million dollars to establish a research center to better develop molecular models of influenza. ^[10]

Herd immunity and mandatory vaccination

An important concept in vaccine planning is herd immunity. This is the idea that when a certain percentage of a population is vaccinated, those within the population who are not vaccinated are protected from the disease. This is a fairly straight forward concept; if 90 percent of a population is immune, then the chances that a carrier of the disease will come into contact with a non-immune member of the population (or "herd") is low. ^[11]. Herd immunity is the goal of most vaccination programs as it is the point where a disease can start to be eliminated altogether from a population.

For example, in 1962 Japan instituted mandatory vaccination against influenza in school children. This continued until 1987 when the program was changed to optional; it was abandoned in 1994. Approximately 85 percent of children were estimated to have been vaccinated. ^[12] Several studies examined the mortality rates due to influenza during this period of time and revealed that the death rates due to influenza in all population groups was drastically decreased, including older adult populations. Since there was no increased rate of vaccination in these populations, the decreased mortality was caused by herd immunity effects of vaccinating so many children. ^[13] Many researchers have written that this and other evidence argues strongly for mandatory vaccination programs world wide as a means of controlling many diseases and preventing a pandemic.^[14]

The USA has mandatory vaccination according to an official CDC schedule. Enforcement is left to the states. Most states have medical and religious exemptions. Some states make it very easy to opt out of vaccines, while other states strictly enforce compliance for school attendance. The difference in vaccination rates between these states is actually very slight, and not nearly enough to affect herd immunity.

Adverse Reactions

Vaccines are not completely harmless, and many have a significant morbidity and mortality associated with them. Postvaccinial encephalitis is a known hazard of smallpox vaccine, for example. A recently-introduced vaccine against human papilloma virus, the causative agent of cancer of the uterine cervix, has now been linked to a number of sudden deaths reported within days of its administration.^[15]

See also

• Vaccine Injury Compensation Program
• Vaccine Adverse Event Reporting System

References

1. ↑ http://www.cdc.gov/vaccines/pubs/pinkbook/downloads/appendices/B/excipient-table-2.pdf
2. ↑ http://www.nvic.org/state-site/state-exemptions.htm
3. ↑ http://www.vaccinesafety.edu/cc-exem.htm
4. ↑ http://www.howstuffworks.com/immune-system7.htm How stuff works: Antibodies
5. ↑ http://www.drspock.com/article/0,1510,4866,00.html The Main Types of Vaccine
6. ↑ http://www.associatedcontent.com/article/183349/soldier_infects_toddler_son_with_lifethreatening.html AP article on eczema vaccinatum
7. ↑ "Inactivated Influenza Vaccine, What you need to know," a publication of the Center for Disease Control, 2006. Available online at: http://www.cdc.gov/nip/publications/VIS/vis-flu.pdf
8. ↑ http://www.nature.com/nrd/journal/v5/n3/full/nrd1988.html Influenza vaccines
9. ↑ http://www.nature.com/news/2003/030324/full/030324-5.html Flu changes modeled
10. ↑ http://www.spiritindia.com/health-care-news-articles-8024.html $26 million NIH contract to establish new flu/bird flu Center of Excellence
11. ↑ http://www.mathepi.com/maindir/herd.html The mathematics of herd immunity
12. ↑ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=387431 Control of Influenza
13. ↑ http://www.newsrx.com/newsletters/Vaccine-Weekly/2001-04-11/200104113335VW.html Mandatory Vaccination of Japanese Schoolchildren Demonstrates "Herd Immunity"
14. ↑ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1360502 Herd Immunity
15. ↑ Cockcroft, Lucy, "Cervical cancer drug Gardasil linked to deaths," London Daily Telegraph, October 29, 2007. Retrieved November 10, 2007.