Immunisations

The terms immunisation, inoculation, and vaccination all refer to the process whereby a pathogen is introduced into the body to produce or strengthen immunity to a specific disease or condition.

There are a number of ways to construct a vaccine, but they all work in essentially the same way: by trying to provoke an immune system response to a particular pathogen. If successful, memory cells within the immune system are primed to respond quickly in attacking and clearing an infectious agent when there is real exposure.

Vaccinations can be delivered various ways, including intradermal, subcutaneous, or intramuscular injection; intranasal spray; oral administration; skin puncture using an instrument with multiple short tines; and through placing a drop of a substance on the skin and making multiple scratches.

There are several different types of vaccines, each with its own advantages and drawbacks. 

• Live attenuated vaccines contain a living version of the infectious microbe, but in a weakened form so that it does not cause actual disease. Viral vaccines have been made to prevent measles, mumps, and chickenpox.  Inactivated vaccines contain the infectious microbe, but it has been killed through chemicals, radiation, or heat. 
• Sub-unit vaccines do not contain the entire microbe, but anywhere from one to twenty of its antigens that are thought to be most likely to stimulate an immune response. Polio is this type of vaccine.
• Toxoid vaccines are used against bacteria that secretes toxins. The toxin is inactivated through treatment with formalin to create the vaccine. Examples of this type are tetanus and diphtheria vaccines.
• Conjugate vaccines are a special type of subunit vaccine that helps immune systems recognise bacteria that has a polysaccharide coating. Antigens or toxins from a recognised microbe is linked to the polycacchaarides. The Haemophilus influenzae type B is an example of this type.
• DNA vaccines do not use the actual microbe, just its genetic material. Clinical trials are in process against the viruses that cause herpes and influenza.
• Recombinant vector vaccines are similar to DNA vaccines, but employ a virus or bacterium as a vector to carry the microbial DNA to the body's cells. This technology is currently being used to create a vaccine to protect against cholera.

There are particular issues to consider concerning immunisations for people with HIV. Although killed vaccines and sub-unit vaccines are perfectly safe for HIV-positive people because they contain no infectious matter, there is a danger that a damaged immune system may not be able to control even the weakened or low doses of organisms found in live attenuated vaccines.