Immunisation – protecting our children from disease
Box 3 | The basics of making a vaccine
Edward Jenner used the first vaccine 200 years ago. He injected people with cowpox, a mild disease, so they were protected against smallpox, a much more serious disease (Box 1). Since then, this practice of deliberately infecting people with a mild disease to provide protection against a more serious form of the disease has become commonplace.
To make vaccines that produce the mild form of a disease, the disease-causing agent (the pathogen) must first be isolated and then treated so that it stimulates an immune response in the body but does not cause the disease.
Obtaining the pathogen
Conventional methods of producing vaccines involve growing large quantities of the pathogen. Viruses, for example, are cultivated by infecting cells grown in tissue culture, while many bacteria can be grown on agar gels. The pathogen is then concentrated, purified and treated to inactivate its capacity to cause disease.
Inactivating the pathogen
The pathogen can be inactivated using one of several techniques:
- It can be weakened by ageing it or altering its growth conditions (such as by depriving it of an essential nutrient). This technique produces a live, attenuated (weakened) vaccine. The vaccines for measles, mumps, and rubella are prepared in this way. Because this vaccine is actually a living microbe, it multiplies within your body and therefore causes a strong stimulation of the immune system.
- It can be killed with formalin or by exposure to a high temperature. This method produces a killed vaccine. The vaccine for typhoid is prepared in this way. Because killed vaccines don’t multiply in your body, you require a number of injections to produce a high enough level of immunisation to protect fully against the disease.
- Parts of the pathogen (antigens) that stimulate an immune response can be separated from the pathogen and used as a vaccine. This produces a subunit vaccine. The Haemophilus influenza type b and the new whooping cough vaccine are prepared in this way. These vaccines are examples of ‘acellular’ vaccines because they don’t contain whole cells of the pathogen.
Adjuvants
Most killed vaccines do not work unless an adjuvant is added. Adjuvants strengthen the immune response in some way. Most adjuvants currently used are compounds containing aluminium.
New vaccines
Medical researchers continue to pursue new methods of producing vaccines, particularly using biotechnology and genetic engineering techniques. These techniques can eliminate the need to produce large quantities of the microorganism in order to make a vaccine.
Boxes
Box 1. Acquired immunity: The body's second line of defence
Box 2. Smallpox – the eradication of a disease
Box 4. WHO's Global Programme for Vaccines and Immunization
Box 5. A controversial history
Related sites
The future of vaccines (Nova: Science in the news, Australian Academy of Science)
Development of polio vaccines (Access Excellence)
The Science of
Immunisation: Questions and Answers (Australian Academy of Science)
Update November 2012.