Vaccination questions answered

Vaccination protects individuals and communities

Vaccination protects individuals and communities

What’s the difference between immunisation and vaccination?
Vaccination means having a vaccine. Immunisation means both receiving a vaccine and becoming immune to a disease, as a result of being vaccinated.

Most people use the terms “vaccination” and “immunisation” interchangeably, but their meanings are not exactly the same.

How does immunisation work?
All forms of immunisation work in the same way. When a person is vaccinated, their body produces an immune response to the vaccine in the same way that it would after being infected by a disease – but without the person suffering symptoms of the disease. When a person comes into contact with that disease in the future, their immune system will respond fast enough to prevent the person developing the disease, or serious complications of the disease.

What is in vaccines?
Vaccines contain small doses of either:

  • a live but weakened virus;
  • a killed bacteria or virus, or small parts of bacteria; or
  • 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. Since 2000, vaccines available in most developed countries have not contained thiomersal. Some vaccines may also contain a small amount of an aluminium salt, which helps to produce a better immune response.

How safe are vaccines?
Before vaccines are made available for use, they are rigorously tested in thousands of people in progressively larger clinical trials. These trials are strictly monitored for safety. The approval process for a vaccine can take up to 10 years.

Why do children get so many immunisations?
A number of immunisations are required in the first few years of a child’s life to protect them against the most serious infections of childhood. The immune system in young children does not work as well as the immune system in older children and adults, because it is still immature. Therefore, more doses of vaccine are often needed.

Another reason why children get many immunisations is that new vaccines against serious infections continue to be developed. However, the number of injections is also being reduced by the use of combination vaccines, where several vaccines are combined into one injection.

Why should children be immunised?
There are two reasons for immunising every child:

1. Immunisation is the safest and most effective way of providing protection against the disease. After immunisation, your child is far less likely to catch the disease if there are cases in the community and if it is caught, they are likely to only have mild symptoms. The benefit of protection against the disease far outweighs the risks of immunisation.

2. If enough people in the community are immunised, the infection can no longer be spread from person to person. This is how smallpox was eliminated from the world and polio has disappeared from many countries.

Do children’s vaccines contain mercury (thiomersal)?
Thiomersal (or thimerosal) is a preservative that contains a form of mercury. Thiomersal is partly composed of mercury in the form of ethylmercury. It was used in very small amounts in vaccines from the 1930s onwards, to prevent bacterial and fungal contamination. Many comprehensive studies and reviews by expert panels have shown that there is no evidence of developmental or neurological abnormalities, such as autism, having resulted from the use of vaccines containing thiomersal. Nonetheless, thiomersal was removed from childhood and adolescent vaccines as a precautionary measure.

How long do immunisations take to work?
In general, the normal immune response to vaccines takes approximately two weeks to work. This means that protection from an infection will not occur immediately after immunisation.

Some vaccines need to be given a number of times to build long-lasting protection. For example, a child who has been given only one or two doses of diphtheria-tetanus-pertussis vaccine (DTPa) is only partially protected against diphtheria, whooping cough and tetanus, and may become sick if exposed to these diseases. However, some vaccines give protection after only one dose.

How long do immunisations last?
The protective effect of some immunisations can last up to 30 years. Other immunisations are required more often, such as influenza immunisation which is need annually due to frequent changes to the type of influenza virus circulating in the community. In addition, booster doses are needed for some vaccines because immunity decreases over time.

Does my teenager need to be immunised?
Some vaccines, such as Human papillomavirus (HPV) vaccine, are not needed by children but are required by adults. HPV immunisation has the greatest benefit when administered in early adolescence.

The effect of some vaccines administered in early childhood, such as pertussis and hepatitis B, wane over time. A booster is required to ensure continued protection from these diseases.

Is everyone protected from disease by immunisation?
Immunisation not only protects vaccinated individuals, but it also helps protect the entire population (for example those who are too young to be vaccinated or those that are not able to be vaccinated for medical reasons). For immunisation to provide the greatest benefit, a sufficient number of people (around 90 percent for most diseases) need to be vaccinated to halt the spread of bacteria and viruses that cause disease – a phenomenon called “herd immunity”.

Even when all the doses of a vaccine (the course) have been given to an individual, not everyone is protected against the disease.

Measles, mumps, rubella, tetanus, polio and Haemophilus influenzae type B (hib) vaccines protect more than 95 percent of children who have completed the course. One dose of meningococcal C vaccine at 12 months protects over 90 percent of children. Three doses of whooping cough (pertussis) vaccine protect about 85 percent of children who have been immunised, and will reduce the severity of the disease in the other 15 percent if they do catch whooping cough.

The protection levels provided by vaccines differ. For example, if 100 children are vaccinated with the measles, mumps, rubella vaccine, 5-10 of the fully immunised children might still catch measles, mumps or rubella (although the disease will often be milder in immunised children). However, if you do not immunise 100 children with MMR vaccine, and the children are exposed to measles, most of them will catch the disease with a high risk of complications, such as lung infection (pneumonia) or inflammation of the brain (encephalitis).

Are there any reasons to delay immunisation?
There are very few medical reasons to delay immunisation. If a person is sick with a high temperature (over 38°C) then immunisation should be postponed until the person is recovering. A child who has a runny nose but does not have a high temperature can be immunised, as can a child who is on antibiotics and obviously recovering from an illness. Talk to your immunisation provider if you are unsure.

What are the side-effects of immunisation?
Many children experience minor side effects following immunisation. Most side effects last a short time and the child recovers without any problems. Common side effects of immunisation are redness, soreness and swelling at the site of an injection, mild fever, and grizzly or unsettled behaviour. You should give your child extra fluids to drink, not overdress babies if they are hot, and consider using paracetamol to help ease the fever and soreness.

Although serious reactions to immunisation, such as febrile seizures, are very rare, if they do occur you should consult your doctor immediately.

Why is it important for all children to be immunised?
Immunisation is a simple, safe and effective way of protecting a child from diseases that can cause serious illness and sometimes death. If most children are vaccinated, this indirectly protects people who are still susceptible to the disease as they are less likely to come into contact with someone who is carrying the pathogens – a concept known as herd immunity.

Herd immunity can protect those who are too young to be vaccinated or cannot be vaccinated because of medical conditions (eg receiving chemotherapy), and those who do not respond adequately to immunisation. The more people who vaccinate their children, the greater our ability to control serious vaccine preventable diseases.

What is herd immunity?
An important feature of immunisation is that it brings benefits not only for the individual who receives the vaccine, but also for the entire population through a concept known as herd immunity, sometimes also called community immunity. If enough people are immunised and protected from a disease, the infection will not be able to spread. This protects the population as a whole from infection. Herd immunity is important for those who cannot receive vaccinations.

These include children who are too young to be vaccinated, people with immune system problems and those too ill to receive vaccines. The proportion of the population which must be immunised in order to achieve herd immunity varies for each disease but can be up to 95 percent for some highly infectious diseases, such as measles. The underlying principle is the same: once enough people are protected, they help to protect vulnerable members of the community by reducing the spread of disease.

Can immunisation overload the immune system?
No. Children and adults come into contact with many antigens (substances that provoke a reaction from the immune system) each day, and the immune system responds to each antigen in specific ways to protect the body. Without a vaccine, a child can only become immune to a disease by being exposed to infection, with the risk of severe illness. If illness occurs after vaccination, it is usually insignificant.

Why is immunisation still necessary in this day and age?
Immunisation is the safest and most effective way of giving protection against vaccine-preventable diseases. After immunisation, a person is far less likely to catch the disease if there are cases in the community.

If enough people in the community are immunised, the infection can no longer be spread from person to person. For example, smallpox was officially declared eradicated in 1980 after a concerted campaign of surveillance and vaccination led by the World Health Organisation. A similar campaign by the Global Polio Eradication Initiative has succeeded in reducing polio cases with only a few isolated cases remaining in the developing world. –