Lesson 6

How do vaccines work?

Learning outcomes & key terms

  • 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.

This page is to be used as a reference point. A structured online course and quiz can be accessed by clicking the button below.

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What is a vaccine?

A vaccine contains an altered version of a pathogen or it’s toxin. The altered state of the pathogen could be weakened or dead. Sometimes only a pat of the pathoigen 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.

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

Herd Immunity

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

  • Delete unwanted extra (trivial) details that can go without losing the overall sense
  • Delete information that is repeated in some way
  • Replace the details with more general terms or descriptions
  • Select a topic sentence or create 1 if it is missing
  • Check there is sufficient detail to make sense

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.