How does immunisation work?
The terms ‘vaccination’ and ‘immunisation’ don’t mean quite the same thing. Vaccination is the term used for getting a vaccine — that is, actually getting the injection or taking an oral vaccine dose. Immunisation refers to the process of both getting the vaccine and becoming immune to the disease following vaccination.
All forms of immunisation work in the same way. When someone is injected with a vaccine, their body produces an immune response in the same way it would following exposure to a disease but without the person getting the disease. If the person comes in contact with the disease in the future, the body is able to make an immune response fast enough to prevent the person developing the disease or developing a severe case of the disease.
What is in vaccines?
Some vaccines contain a very small dose of a live but weakened form of a virus. Some vaccines contain a very small dose of killed bacteria or small parts of bacteria, and other vaccines contain a small dose of a modified toxin produced by bacteria.
Vaccines may also contain either a small amount of preservative or a small amount of an antibiotic to preserve the vaccine. Some vaccines may also contain a small amount of an aluminium salt, which helps produce a better immune response.
How long do immunisations take to work?
In general, the normal immune response takes approximately 2 weeks to work. This means protection from an infection will not occur immediately after immunisation. Most immunisations need to be given several times to build long-lasting protection.
A child who has been given only 1 or 2 doses of the DTPa vaccine is only partially protected against diphtheria, tetanus and pertussis (whooping cough) and may become sick if exposed to these diseases until they have all the doses they need. However, some of the new vaccines, such as the meningococcal ACWY vaccine, provide long-lasting immunity after only one dose.
How long do immunisations last?
The protective effect of immunisations is not always lifelong. Some, like tetanus vaccine, can last up to 10 years depending on your age, after which time a booster dose may be given. Some immunisations, such as whooping cough vaccine, give protection for about 5 years after a full course. Influenza immunisation is needed every year due to frequent changes to the type of flu virus in the community.
Is everyone protected from disease by immunisation?
Even when all the doses of a vaccine have been given, not everyone is protected against the disease. Measles, mumps, rubella, tetanus, polio, hepatitis B and haemophilus influenzae type b (Hib) vaccines protect more than 95% of children who have completed the course. One dose of meningococcal ACWY vaccine at 12 months protects over 90% of children.
Three doses of whooping cough vaccine protect about 85% of children who have been immunised, and will reduce the severity of the disease in the other 15% if they do catch whooping cough. Booster doses are needed because immunity decreases over time.