What is a vaccine?

A vaccine is an antigen preparation used in artificial immunisation. Vaccination is the artificial introduction of pathogenic organisms so that the ability to produce the appropriate antibodies is acquired without the person having to suffer from the effects of the disease.

The purpose of immunisation is to prevent people from getting sick. It helps to protect people against the complications of becoming ill, including developing chronic diseases, cancer, and death. Vaccines work by stimulating the body's defence mechanisms to provide protection against infection.

What are the four traditional types of vaccines?

1. Live attenuated vaccines: Living attenuated microorganisms are microorganisms of reduced virulence, that is, microorganisms with a reduced ability to produce disease system, therefore, the immunised person does not contract the disease but manufactures antibodies against the antigen.

2. Inactivated vaccines: Contains dead microorganisms, and they produce immunity that is shorter lasting than immunisation using live attenuated microorganisms.

3. Toxoid vaccines: In cases where bacteria produce their effects in humans by liberating toxins, it is not necessary to use the bacteria for immunisation as the toxins produced by bacteria can be inactivated, so that when they are injected into someone, they do not make the person ill.

4. Sub-unit vaccines: Instead of using a whole dead or attenuated microorganism, a fragment of the organism can be used to provoke the immune response.

What processes take place following vaccination?

When given a vaccination, the antigens contains within the vaccine are detected by a B-lymphocyte in a lymph node which becomes sensitised, enlarges and divides, forming clones. This process is fairly slow on the first exposure to the antigen. Due to the attenuated nature of the pathogens, no or very few symptoms of the disease being vaccinated against occurs. Symptoms occur before enough clones are made to produce antibodies (when naturally exposed). Symptoms decrease as antibody levels rise. Some of the clones remain in the original lymph node as B-lymphocyte memory cells, others migrate to other lymph nodes.