Misplaced Pages

Revision as of 19:25, 3 April 2005

A vaccine is an antigenic preparation used to produce active immunity to a disease, in order to prevent or ameliorate the effects of infection by any natural or 'wild' strain of the organism. The term derives from vaccinia, the infectious viral agent of cowpox, which, when administered to humans, provided them protection against smallpox.

Types of vaccines

Vaccines may be living, weakened strains of viruses or bacteria which intentionally give rise to inapparent-to-trivial infections. Vaccines may also be killed or inactivated organisms or purified products derived from them.

In recent years a new type of vaccine created from infectious agent's DNA, called DNA vaccination has been developed. It works by inserting the DNA coding for a part of a virus or a bacterium that is recognizable by the immune system is inserted and expressed in human/animal cells. These cells then develop immunity against the infectious agent, without the effects other parts of a weakened agent might have. As of 2003, DNA vaccination is still experimental, but shows some promising results.

Live but weakened (attenuated) vaccines are used against measles, rubella, mumps, chicken pox (varicella), rabies, polio, yellow fever and smallpox (actually cowpox virus); killed agents are used against influenza, polio, hepatitis A, cholera and typhoid; toxoids against diphtheria and tetanus. The live tuberculosis vaccine is not the contagious TB strain, but a related strain called "BCG"; it is used in the United States very infrequently.

Developing immunity

The immune system recognizes the vaccine contents as foreign, destroys them, and 'remembers' them. When the virulent version of the agent comes along, the immune system is thus prepared to respond, by (1) neutralizing the agent before it can enter cells, and (2) by recognizing and destroying infected cells before the agent can multiply to vast numbers.

Vaccines have contributed to the eradication of Smallpox, one of the most contagious and deadly diseases known to man. Other diseases such as rubella, polio, measles, mumps, chickenpox, and typhoid are no where near as common as they were just a hundred years ago. As long as the vast majority of people are vaccinated it is relatively much more difficult for an outbreak of disease to occur, let alone spread. This effect is called herd immunity.

Controversy surrounding the use of vaccines

Prior to 1997 a number of vaccines, including those given to very young children, used thimerosal, a preservative contained trace amounts of mercury. In sufficient quantities, mercury has deleterious neurological effects. It was (and in some cases still is) used in some DTP (diphtheria, tetanus and pertussis) vaccine formulations.

In the late 1990s, vaccines became the target of controversy in both the US and the United Kingdom when a small study conducted by Dr. Andrew Wakefield linked the MMR vaccine to autism. The Wakefield study garnered media attention and caused concern in the minds of many parents leading to a drop in the uptake of the MMR vaccine in the UK and some other countries. The study also garnered criticism for its small sample size, and for failing to use healthy controls. In response to the controversies a number of studies with larger sample sizes were conducted. In 2004, 10 of the 13 authors of the original Wakefield study retracted the paper's interpretation, stating that the data were insufficient to establish a causal link between MMR vaccine and autism. Also in 2004, the United States' Institute of Medicine reported that evidence pointed away from a link between vaccines containing thiomerosal and children who developed autism.

Potential for adverse side effects in general

Some people, particularly those who practice alternative medicine, refuse to immunize themselves or their children, because they believe vaccines' adverse side effects outweigh their benefits. A variation of this reasoning is that not enough is known of the adverse effects to determine whether the potential benefits make the risks worthwhile. Since most people are vaccinated against contagious and potentially fatal diseases, the chances of someone who is not vaccinated becoming ill is a good deal smaller than it might be if their opinion was held by more people. Thus, they reap some of the benefits of vaccines, through herd immunity, without assuming most of the risks.

Advocates of routine vaccination argue that side effects of approved vaccines, whilst real, are either far less serious than actually catching the disease, or are very rare, and argue that the calculus of risk/benefit ratio should be based on benefit to humanity rather than simply on the benefit to the immunized individual. The main risk of rubella, for example, is to the fetuses of pregnant women, but this risk can be effectively reduced by the immunization of children to prevent transmission to pregnant women.

See also

• AIDS vaccine
• Edward Jenner
• genetics
• iatrogenesis
• immunization
• immunology
• inoculation
• medicine
• Timeline of vaccines
• vaccination
• Vaccines and Fetal Tissue

External links

• "Thimerosal and the Occurrence of Autism: Negative Ecological Evidence From Danish Population-Based Data" PEDIATRICS Vol. 112 No. 3 September 2003 - This study shows an increase in autism after the discontinuation of the thimerosal formulations of the MMR vaccine in the Danish population.
• NIH.gov - National Intitutes of Health (conventional medical opinion on vaccination)

• Wakefield and colleagues

• Virology
• Infectious diseases