Friday, May 25, 2007

Vaccines and Immunisation

Vaccines and Immunisation

Many infectious diseases, including most of the common viral infections, occur only once during a person's lifetime. The reason is that the antibodies produced in response to the disease remain afterwards, prepared to repel any future invasion as soon as the first infectious germs appeared. The duration of such immunity varies, but it can last a lifetime.

Protection against many infections can now be provided artificially by the use of vaccines derived from altered forms of the infecting organism. These vaccines stimulate the immune system in the same way as a genuine infection, and provide lasting, active immunity. Because each type of microbe stimulates the production of a specific antibody, a diffferent vaccine must be given for each disease.

Another type of immunisation, called passive immunisation, relies on giving antibodies.

Why They Are Used

Some infectious diseases cannot be treated effectively or are potentially so serious that prevention is the best treatment. Routine immunisation not only protects the individual but may gradually eradicate the disease completely, as has been achieved with smallpox.

Newborn babies receive antibodies for many diseases from their mothers, but this protection lasts only for about three months. Most children between the ages of 2 months to 15years are routinely vaccinated against common childhood infectious diseases. In addition, travellers to many under developed countries, especially those in the tropics, are often advised to be vaccinated against the diseases common in those regions.

Effective lifelong immunisation can sometimes be achieved by a single dose of the vaccine. However, in many cases, reinforcing doses, commonly called booster shots, are needed later to maintain reliable immunity.

Vaccines do not provide immediate protection against infection and it may be up to four weeks before full immunity is able to develop. When immediate protection from infectious disease is needed— for example, following exposure to infection — it may be necessary to establish passive immunity with immune globulins.

How They Work

Vaccines provoke the immune system into creating antibodies that help the body to resist specific infectious diseases. Many vaccines (known as live vaccines) are made from artificially weakened forms of the disease-causing germ.

Common Vaccinations

Most vaccinations are given during infancy and childhood as part of a routine immunisation schedule. Most are given by germs and are effective in stimulating sufficient growth of antibodies. Other vaccines rely either on inactive (or killed) disease-causing germs, or inactive derivatives of these germs, but their effect on the immune system remains the same. Effective antibodies are created, thereby establishing active immunity.

How They Affect You

The degree of protection varies among different vaccines. Some provide reliable lifelong immunity; others may not give full protection against a disease, or the effects may last for as little as six months. Influenza vaccines usually protect only against the variety of virus causing the latest outbreak of flu. New varieties appear during most years. Those people at particular risk through their work or travel can have additional immunisation in adulthood. Any vaccine may cause side-effects but they are usually mild and soon disappear. The most common reactions are a red, slightly raised, tender area at the site of injection and a slight fever or a flu-like illness lasting for one or two days.

Risks And Special Precautions

Serious reactions are rare and, for most children, the risk is far outweighed by the protection given. Children who have had fits may be advised against vaccinations for pertussis (whooping cough) or measles. Children who have any infection more severe than common cold will not be given any routine vaccination until they have recovered.



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