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Te āhua o te mahi o ngā rongoā āraimate 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 cannot 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, 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 are less likely to get sick.

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Why you need extra doses

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

When you are 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 is 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 — there are no safety concerns with having multiple vaccines at the same time.

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  • These contain just enough of the bacteria or virus to stimulate an immune response. The bacteria or virus have been weakened so that they can't cause disease.

    Live vaccines include the:

    • measles, mumps and rubella (MMR) vaccine
    • rotavirus vaccine
    • chickenpox vaccine
    • tuberculosis (BCG) vaccine.

    Live vaccines have been used in Aotearoa New Zealand for over 50 years, including measles-containing vaccines since 1969.

  • These contain bacteria or viruses that have been killed or inactivated. With inactivated vaccines, you usually need more doses to give full protection against disease.

    Inactivated vaccines include:

    • the polio vaccine
    • some flu vaccines
    • the hep A vaccine.

  • These contain parts of bacteria or viruses that have been made harmless.

    Subunit vaccines include the:

    • diphtheria vaccine
    • hep B vaccine
    • HPV vaccine
    • Hib vaccine
    • meningococcal vaccine
    • pneumococcal vaccine.

  • The Pfizer COVID-19 vaccine is a type of mRNA vaccine. It does not contain any virus. Instead, it contains a molecule called mRNA that has instructions for making a protein on the surface of the COVID virus.

    The mRNA from the vaccine does not stay in your body, but is broken down shortly after vaccination.

    Learn more about different types of vaccines – Healthify

Vaccines safety

Before any vaccine is approved for use, it goes through a long and rigorous testing process by scientists around the world and in Aotearoa 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 have not.

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

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