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 prevent diseases. Being vaccinated causes your body to produce antibodies. This means that if you are infected with a disease (from a cough, sneeze, blood, etc), these protective antibodies are already in your bloodstream to quickly fight off the germs. Even if vaccinated people do get sick from the disease, they usually get a mild form of that disease – and recover faster and are less likely to have serious complications.

Babies are born with immunity to some infections because their mother’s antibodies are passed on to them in the womb, but this immunity does not last long. Babies get more immunity from being breastfed and, as they grow, they need vaccinations at specific ages to protect them from many life-threatening diseases. Read more about vaccine-preventable diseases.

(Ministry of Health, NZ, 2020)

What are the types of vaccines?

There are generally 3 types of vaccines.

Type of vaccine Description
Live vaccines
  • These contain bacteria or viruses that have been weakened so that they can't cause disease. 
  • After vaccination, 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 are taking medicines that can weaken your immune system. 
Dead (or inactivated) vaccines 
  • These 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 vaccination 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
  • These contain parts of bacteria or viruses or bacterial toxins that have been made harmless.
  • Examples of these vaccines include:
    • diphtheria 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 your body respond to the vaccine. The very small amount of these ingredients does not cause any harm. Learn more about what ingredients are in a vaccine.

When should you get vaccinated?

The National Immunisation Schedule has a list of free vaccinations for different ages. Vaccinating 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. Vaccination 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 and learn more about side effects from vaccines.

How effective are vaccines?

Studies have shown that if all recommended doses of vaccines are given, they will protect 80–98% of the children who are vaccinated. For example, pertussis (whooping cough) vaccine is effective in about 84% of children and the measles vaccine in 90–98% 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 vaccinated and people who cannot be vaccinated because they are unwell. About 95% of people in the community need to be vaccinated to protect the whole community against diseases like measles. Learn more about worldwide protection.

A very small number of people who are vaccinated don't 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 vaccinated.

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 about the effectiveness of vaccines.

Where can I get vaccinated?

The best place to go for vaccinations is your family medical clinic. They have your medical records and can check to see if you’ve already had a particular vaccination. Either your doctor or a nurse can give the vaccination.

If you don’t have a family doctor, you can go to one of the after-hour medical clinics. Phone them first to make sure they can help you with the vaccination you need.

You can find a clinic near you on the Healthpoint website. Put in your address and region, and under Select a service, click on GPs/Accident & Urgent Medical Care.

Vaccines on the National Immunisation Schedule are free. Other vaccines are funded only for people at particular risk of disease. You can choose to pay for vaccines that you are not eligible to receive for free.

Learn more

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


  1. Childhood immunisation HealthEd, NZ
  2. Types of vaccines Immunisation Advisory Centre, NZ
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 29 Sep 2020