How do they work? Who needs them? Are there any risks?

Vaccinations are one of the best ways to protect against many serious diseases.

How do vaccines work?

Vaccines work by stimulating your immune system to produce antibodies against diseases. This means that if your child comes across the disease, protective cells and antibodies are already there to quickly fight off the germs. Even if your child does get sick from the disease, they usually get a mild form of the disease – they recover faster and are less likely to have serious complications. Vaccines prevent diseases.

Babies are born with immunity to some infections from antibodies passed on to them from their mother before birth, but this immunity does not last long. Babies and children need immunisations on time to protect them from many life-threatening diseases. Read more about vaccine-preventable diseases.

(Ministry of Health NZ, 2017)

What are the types of vaccines?

There are generally 3 types of vaccines.

Type of vaccine Description
Live vaccines
  • Contain bacteria or viruses that have been weakened so that they cannot cause disease. 
  • After immunisation, the weakened vaccine viruses or bacteria replicate (grow) in the vaccinated person. This small amount of virus or bacteria can stimulate an immune response.
  • Examples of these vaccines include:
    • measles, mumps and rubella vaccine (MMR)
    • rotavirus vaccine
    • chickenpox vaccine. 
  • Live vaccines are not recommended if you are pregnant or have a very weak immune system from active cancer, leukaemia, lymphoma, HIV or taking medicines that can weaken your immune system etc. 
Dead (or inactivated) vaccines 
  • Contain bacteria or viruses that have been killed or inactivated. 
  • They can be safely given to a person with a weakened immune system. However, a person with an impaired immune system response may not develop the same amount of protection after immunisation as a healthy person receiving the vaccine.
  • With inactivated vaccines, you usually need many doses to give full protection against diseases.
  • Examples of these vaccines include:
    • polio vaccine
    • some influenza vaccines
    • hepatitis A vaccine
Subunit vaccines
  • Contain parts of bacteria or viruses or bacterial toxins that have been made harmless. 
  • Examples of these vaccines include:
    • diphtheria vaccine
    • tetanus vaccine
    • hepatitis B vaccine
    • human papillomavirus (HPV) vaccine
    • Haemophilus influenzae type b vaccine
    • meningococcal vaccine
    • pneumococcal vaccines 

Vaccines may also contain other ingredients such as preservatives, and ingredients that help the body respond to the vaccine. The very small amount of these ingredients do not cause any harm.

When should you get vaccinated?

The National Immunisation Schedule has a list of free vaccinations for different ages. Immunising on time gives the best protection. Missing or late vaccinations can put your family’s health at risk. 

Most vaccines are given to babies and children to build up their immunity. Immunisation starts at 6 weeks old. Other vaccines are recommended for people who are at greater risk of certain diseases, such as people with a weakened immune system because of illness or the medicines they are taking, the elderly or people who are travelling overseas where certain diseases are more common.

Are there any risks to being vaccinated?

Most reactions to vaccines are mild, such as fever or redness at the injection site. These reactions show that the immune response is building and the vaccine is working. Very rarely, a serious allergic reaction (anaphylaxis) can happen. This is treatable and occurs soon after the injection. This is why you must wait at the doctor's clinic for 20 minutes after vaccination. If you are worried, contact your doctor straight away. Read more about comparison of possible disease complications and vaccine responses

How effective are vaccines?

Studies have shown that if all recommended doses of vaccines are given, they will protect 80% to 98% of the children who are immunised. For example, pertussis (whooping cough) vaccine is effective in about 84% of children and the measles vaccine in 90% to 98% of children.1

Vaccination is an important part of protecting the community against disease. This helps to lower serious infections spreading and protects babies who are yet to be fully immunised and people who cannot be immunised because they are unwell. About 95% of people in the community need to be immunised to protect the whole community against diseases like measles.

A very small number of children who are immunised do not develop strong immunity and they may still become ill with one of the diseases. If that happens, they usually have a milder illness than people who have not been immunised. More than one dose of some vaccines is needed for full protection. Booster doses of vaccines may be also be needed for some diseases to stay protected.    

Learn more

Immunisation overview Immunisation Advisory Centre, NZ 
How vaccinations work NHS Choices, UK
Diseases and vaccines Ministry of Health, NZ
Vaccine administration Immunisation Advisory Centre, NZ


  1. Childhood immunisation HealthEd, New Zealand
  2. Types of vaccines Immunisation Advisory Centre
Credits: Editorial team. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 13 Dec 2017