Vaccine

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(Redirected from Vaccines)

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. The process of distributing and administrating vaccines is referred to as vaccination.

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Origin of vaccines

In 1796, during the heyday of the smallpox virus in Europe, an English country doctor, Edward Jenner, observed that milkmaids would sometimes become infected with cowpox through their interactions with dairy cows' udders. Cowpox is a mild relative of the deadly smallpox virus. Building on the foundational practice of inoculation, Jenner took infectious fluid from the hand of milkmaid Sarah Nelmes. He inserted this fluid, by scratching or injection, into the arm of a healthy local eight year old boy, James Phipps. Phipps then showed symptoms of cowpox infection. Forty-eight days later, after Phipps had fully recovered from cowpox, Jenner injected smallpox-infected matter into Phipps, but Phipps did not later show signs of smallpox infection.

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.

There are three types of traditional vaccines[1]:

  • Inactivated - these are previously virulent micro-organisms that have been killed with chemicals or heat. Examples are vaccines against flu, cholera, plague, and hepatitis A. Most such vaccines may have incomplete or short-lived immune responses and are likely to require booster shots.
  • Live, attenuated - these are live micro-organisms that have been cultivated under conditions to disable their virulent properties. They typically provoke more durable immunological responses and are the prefered type for healthy adults. Examples include flu, yellow fever, measles, rubella, and mumps.
  • Toxoids - these are inactivated toxic compounds from micro-organisms in cases where these (rather than the micro-organism itself) causes illness. Examples of toxoid-based vaccines include tetanus and diphtheria

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.

A number of innovative vaccines are also in development and also in use:

  • Conjugate - certain bacteria have polysaccharide outer coats that are poorly immunogenic. By linking these outer coats to proteins (e.g. toxins), the immune system can be led to recognize the polysaccharide as if it were a protein antigen.
  • Subunit - rather than introducing a whole inactivated or attenuated micro-organism to an immune system, a fragment of it can create an immune response
  • Recombinant Vector - by combining the physiology of one micro-organism and the DNA of the other, immunity can be created against diseases that have complex infection processes
  • DNA vaccination - in recent years a new type of vaccine, created from an infectious agent's DNA called DNA vaccination, has been developed. It works by insertion (and expression, triggering immune system recognition) into human or animal cells, of viral or bacterial DNA. These cells then develop immunity against an infectious agent, without the effects other parts of a weakened agent's DNA might have. As of 2003, DNA vaccination is still experimental, but shows some promising results.

Developing immunity

The immune system recognizes vaccine agents as foreign, destroys them, and 'remembers' them. When the virulent version of an agent comes along, the immune system is thus prepared to respond, by (1) neutralizing the target agent before it can enter cells, and (2) by recognizing and destroying infected cells before that 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 nowhere near as common as they were just a hundred years ago. As long as the vast majority of people are vaccinated it is 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

See article: Vaccine controversy

Opposition to vaccination, from a wide array of vaccine critics, has existed since the earliest vaccination campaigns: [2].

Prior to 1997, a number of vaccines, including those given to very young children, used thimerosal, a preservative that metabolizes into ethylmercury. It is used in some influenza, DTP (diphtheria, tetanus and pertussis) vaccine formulations.

In the late 1990s, controversy over vaccines escalated in both the US and the United Kingdom when a study, published in the respected journal Lancet, by Dr. Andrew Wakefield suggested a possible link between bowel disorders, autism and MMR vaccine, and urged further research [3]. His report garnered significant media attention, leading to a drop in the uptake of the MMR vaccine in the UK and some other countries. The study 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, and failed to confirm the findings.[4] [5]. In 2004, 10 of the 13 authors of the original Wakefield study retracted the paper's interpretation, without disputing the central finding of a consistent set of bowel disorders among the autistic study subjects, stating the data were insufficient to establish a causal link between MMR vaccine and autism.[6] In 2004 and 2005, England and Wales have seen an increase in the incidence of mumps infections among adolescents and young adults, which health authorities attribute to a decline in booster shots from 92% to 80%, which they believe is due to the alleged misinformation generated by Wakefield's study [7].

Also in 2004, the United States' Institute of Medicine reported that evidence "favors rejection" of any a link between vaccines containing thimerosal, or MMR, and the development of autism [8].

Potential for adverse side effects in general

Some refuse to immunize themselves or their children, because they believe certain 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 it could be argued that they reap some of the benefits of vaccines, through herd immunity, without assuming the risks those who choose to vaccinate do.

Advocates of recommended routine vaccination argue that side effects of most approved vaccines 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.

Efficacy of vaccines

It's worthwhile to note that vaccines don't guarantee protection from a disease. That is, even having been vaccinated, there is still a remote possibility that a vaccinated person may get the disease. The efficacy or performance of the vaccine is dependent on a number of factors:

  • the disease itself (for some diseases vaccination performs better than for other diseases)
  • the strain of vaccine (some vaccinations are for different strains of the disease) [9]
  • whether one kept to the timetable for the vaccinations
  • some individuals are "non-responders" to certain vaccines, meaning that they do not generate antibodies even after being vaccinated correctly
  • other factors such as ethnicity or genetic predisposition (possibly)

In cases where a vaccinated individual does develop the disease vaccinated against, the disease will most likely be milder than if the individual had not been vaccinated.

Economics of vaccine development

One challenge in vaccine development is economic: many of the diseases most demanding a vaccine, including HIV, malaria and tuberculosis, exist principally in poor countries. Pharmaceutical firms and biotech companies have little incentive to develop vaccines for these diseases because there is so little revenue potential. Most vaccine development to date has relied on "push" funding by government and non-profit organizations, of government agencies, universities and non-profit organizations. To date, there has been very little involvement of private industry on a commercial basis.

Many researchers and policymakers are calling for a different approach, using "pull" mechanisms to motivate industry. Mechanisms such as prizes, tax credits, or advance market commitments could ensure a financial return to firms that successfully developed an HIV vaccine. If the policy were well-designed, it might also ensure that people have access to a vaccine if and when it is developed.

See also

References

External links

Vaccine proponent views

Vaccine safety critical views

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