How vaccines work

Sometimes our immune systems need help to fight diseases. Vaccines train the immune system to produce antibodies that protect us from getting sick.

Vaccines prevent you from getting sick

Diseases can be caused by viruses and bacteria. These are so small that you can’t see them, but they are everywhere. Most are harmless, but some can make you really sick.

Inside your body, your immune system helps fight against diseases caused by viruses and bacteria. Sometimes, though, your immune system needs a little help. Vaccines give your immune system instructions on how to defend itself better so your body will have the right tools for the job, meaning you’re less likely to get sick.

Why you need extra doses

To be fully protected you usually need more than 1 dose of a vaccine.

When you’re first vaccinated, your body learns what to do if it meets a particular virus or bacteria. Your second (and sometimes third or fourth) dose boost your immune system so you will have stronger, and longer-lasting, protection.

Different vaccines protect you for different lengths of time, which is why you may need a booster vaccination to strengthen your immunity.

Some vaccines protect against more than 1 disease

Some vaccines provide protection against more than 1 disease in a single vaccine. For example the measles, mumps, and rubella (MMR) vaccine is just 1 injection. This means fewer vaccination appointments and fewer injections.

It’s not always possible to have a different vaccine if you want protection against only one of the diseases. Your immune system is used to dealing with thousands of viruses and bacteria every day – so there are no safety concerns with having multiple vaccines at the same time.

Different types of vaccine

There are 4 different types of vaccine.



Before any vaccine is approved for use, it goes through a long and rigorous testing process by scientists around the world and in New Zealand to ensure its safety and effectiveness.

This process can take several years and compares the health of people who have been immunised with those who haven’t.

Once approved, the safety of the vaccine is also continuously monitored by Medsafe. As part of this process, the Centre for Adverse Reactions Monitoring at Otago University records reactions reported after vaccinations so that scientists can keep track of any reactions that may occur.

Vaccine side effects, reactions, and safety

Why is it important to immunise your tamariki? 

Immunisation basically is a magic therapy. It stimulates your immune system.

It protects against a wide range of illnesses. 

Now, some of those illnesses have gone essentially in our community because immunisation has been so successful.

Why is it important for your child to get all of their immunisations?

It’s really important to get all of the vaccines and not just individual ones.

So if we look at one of the vaccinations, which is called MMR, that is measles, mumps, and rubella. Now, measles is a very severe disease that can kill a large number of children.

Mumps can also kill little children, but it's uncommon.

Rubella is a disease that we haven't seen for such a long period of time. 

Those two, the measles and the rubella have been extremely successful, and if we stop giving those vaccines there's a risk that it can come back.

If a child misses one of their immunisations, can they catch up?

So if you miss one of your child's vaccinations, it's no big deal. Things happen. We all have busy lives. It's really easy to catch up.

The immunisations, again, they're not medicine. There is no overdose that you can have.

So if for whatever reason your child misses the vaccine just present to whoever you want to go to. Typically general practice and say, "Look, my child needs their vaccines," and they can be caught up.

How safe are childhood immunisations?

Childhood immunisations are probably the safest thing that you can ever give your child.

They're much safer than things like paracetamol or ibuprofen, which is something we always give.

The most common side effects you might have from getting an immunisation are things like some pain and swelling around the injection site and sometimes you get a fever.

There are some extremely rare side effects that are very uncommon that we seldom ever see and massively outweighed by the benefits of the immunisations and the protections they give.

Page last updated: 13 Nov 2023