How do vaccines work?

Lesson 6

What is the science behind vaccines?

Learning outcomes

  • Students will understand how vaccines use the bodies immune system to protect against pathogens.
  • Students will understand that there are different types of vaccinations.
  • Students will understand that not everyone can have a vaccine and that herd immunity protects vulnerable individuals.
  • Students will use scientific knowledge and critical thinking and perspective taking skills to evaluate different opinions about vaccination. 


Pathogen: A bacterium, virus, or other microorganism that can cause disease.

Herd immunity: A form of immunity that occurs when a significant part of the population is vaccinated and can provide protection for individuals without sufficient immunity.

Science understanding

Biological sciences

Describing how the requirements for life (for example oxygen, nutrients, water and removal of waste) are provided through the coordinated function of body systems such as the respiratory, circulatory, digestive, nervous and excretory systems.

Explaining how body systems work together to maintain a functioning body using models, flow diagrams or simulations.

Investigating the response of the body to changes as a result of the presence of micro-organisms.

Science as a human endeavour

Scientific understanding, including models and theories, is contestable and is refined over time through a process of review by the scientific community.

Advances in scientific understanding often rely on technological advances and are often linked to scientific discoveries.

People use scientific knowledge to evaluate whether they accept claims, explanations or predictions, and advances in science can affect people’s lives, including generating new career opportunities.

Values and needs of contemporary society can influence the focus of scientific research.

Science enquiry skills

Formulate questions or hypotheses that can be investigated scientifically.

Analyse patterns and trends in data, including describing relationships between variables and identifying inconsistencies.

What is a vaccine?

A vaccine contains an altered version of a pathogen or its toxin.

The altered state of the pathogen could be weakened or dead. Sometimes only a pat of the pathogen is used in a vaccine.

There are new cutting edge vaccines that only use DNA from the pathogen.


How do vaccines work?

A vaccine causes the body to produce antibodies and memory cells that act against the target pathogen, without making the person ill. 

If a vaccinated person is later infected by the same pathogen, their immune system recognises it and can destroy it very quickly.

Vaccines build herd immunity 

Herd Immunity

Herd immunity (also called herd effect, community immunity, population immunity, or social immunity) is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, whether through vaccination or previous infections, thereby providing a measure of protection for individuals who are not immune.

In a population in which a large proportion of individuals possess immunity, such people being unlikely to contribute to disease transmission, chains of infection are more likely to be disrupted, which either stops or slows the spread of disease.

The greater the proportion of immune individuals in a community, the smaller the probability that non-immune individuals will come into contact with an infectious individual, helping to shield non-immune individuals from infection.

Class activity

Scenario 1 – No vaccination

All the students stand up in the room. They must be within arms reach of each other.

Choose one person to have a disease, such as tuberculosis, which is spread through coughing.

They are given a card of red dot stickers which represent TB. (They should also have a red dot sticker on to show that they have the disease).

When they “cough” they pass the card on to the person standing next to them – they have now caught TB and will keep a red dot sticker.

This person then “coughs” and passes the card along.

Eventually the whole class will have been passed the card have a red dot sticker on and have therefore “have” TB.

Scenario 2 – 50% vaccinated

Set the scene as for scenario 1 but this time randomly give 50% of the class green stickers – this means half the children will not be protected.

Now, have the sick person “cough” again but now he can’t pass the red stickers to anyone with a green sticker – they are protected from the immunisation.

Half of the class will be protected. See how far the red sticker can get. 

It will likely still make some children sick, but not all.  This not a full herd immunity but a partial immunity.  

Scenario 3 – 90% vaccinated

Set the scene as for scenario 1 but this time randomly give 90% of the class green stickers – this means only 2 or 3 children will not be protected.

Now, have the sick person “cough” again but now he can’t pass the red stickers to anyone with a green sticker – they are protected from the immunisation.

Most of the class will be protected.

Because the red sticker can’t be passed further than one person at a time, the “unvaccinated” students should be safe.

This is called herd immunity and is vital to protect vulnerable members of our society.


Vaccines protect against an infectious disease. They contain an altered state of the vaccine which stimulates the body to build antibodies to protect against the infection. 

Herd immunity is built when enough people have had a vaccine and have had the infection and survived.