Vaccines work by triggering our immune system to produce disease fighting substances, known as antibodies, without actually infecting us with the disease.

Vaccines contain the same germs that cause disease (for example, measles vaccine contains measles virus, and Hib vaccine contains Hib bacteria). But the germs have been either killed, or weakened to the point that they don’t make you sick. Some vaccines contain only a part of the disease germ.

When a child or adult is vaccinated, the vaccine stimulates their immune system to produce antibodies, exactly like it would if they were exposed to the disease. The child will develop immunity to that disease, but they don't have to get sick first. This is what makes vaccines such a powerful medicine.

Unlike most medicines, which treat or cure diseases, vaccines prevent them.

Video: How a vaccine works MIT Science Out Loud Series

Who are vaccines for?

Certain vaccines are recommended for all children as part of the NZ immunisation schedule. These vaccines protect against diseases that are considered to pose the greatest risk to both the health of individuals and the general population. Eg, polio, meningitis and rubella (German measles)

Other vaccines are recommended for people who are at greater risk of certain diseases, such as those who have low defence against infection, the elderly or those who are travelling overseas where certain diseases are more common.

Are there any risks of vaccines?

There is a small risk of a reaction to a vaccine, especially if you are allergic to animal proteins like eggs, antibiotics, stabilisers or preservatives. In rare cases, reactions to vaccines can be severe or (very rarely) fatal. This is why you are asked to wait 20 minutes in the practice after some receiving some vaccines so you can be observed, and treated, for reactions.

You should not be vaccinated with live vaccines if you are pregnant, have active cancer, leukemia, lymphoma or HIV. However inactivated vaccines are considered safe in these cases. If you have a mild illness such as a cold, earache or diarrhoea, check with your doctor first. 

How effective are vaccines?

Most vaccines are very good at boosting our immune system and protecting us from a wide range of diseases. Some of the biggest advances in medicine have come from widespread vaccination programmes such as the vaccine for polio, TB, measles, mumps, tetanus, haemophilus (causes meningitis and epiglottis) to name a few. Read more about individual vaccines:

Learn more

Immunisation overview Immunisation Advisory Centre (NZ), 2013 
How vaccinations work NHS Choices (UK), 2014
Vaccines and immunisations Centers for Disease Control and Prevention (CDC) (USA), 2010
Diseases and vaccines Ministry of Health (NZ), 2014
Vaccine administration Immunisation Advisory Centre (NZ), 2014
Childhood vaccines: tough questions, straight answers Mayo Foundation for Medical Education and Research, 2013
Parent's guide to Childhood Immunisations Centers for Disease Control and Prevention (CDC), USA.

Credits: Written by Health Navigator NZ, updated May 2017.