Last updated on January 20th, 2023 at 03:41 pm
Vaccines. Something most, if not all of us, are familiar with. MMR (Measles, Mumps & Rubella), TB (Tuberculosis), Smallpox, Chicken Pox, and the more recent HPV (Human Papillomavirus) and Covid-19 vaccines are just a few of the many available to protect us from harmful pathogens (an organism that causes disease like bacteria or viruses – aka ‘germs’). But what exactly is a vaccine, and how does it protect us?
Firstly, to understand vaccines, it helps to have a fundamental understanding of the immune system. The immune system is the body’s natural defence against harmful pathogens. It is a complex system of organs and cells that work together to help fight off infection caused by invading pathogens. When a ‘germ’ enters our body, the immune system triggers a series of responses to identify and destroy it.
Outward signs we are having an immune response are:
- A raised temperature (fever) and uncontrollable shivering (Rigors).
- Inflammation; this can be internal or visible on the skin’s surface – for example, from a cut.
- Coughing & Sneezing (mucus traps germs, which are then removed by the action of coughing or sneezing).
Types of immunity:
Innate (also called nonspecific or natural) immunity: We are born with a combination of physical (skin and mucous membranes in the respiratory and gastrointestinal tracts), chemical (for example, stomach acid, mucous, saliva and tears contain enzymes that breakdown the cell wall of many bacteria1), and cellular (natural killer cells, macrophages, eosinophils are just a few2) defences against pathogens. Innate immunity is a type of general protection designed to immediately respond to the presence of a pathogen.
Adaptive immunity: The adaptive, or acquired, immune response is more specific to an invading pathogen and occurs after exposure to an antigen (a toxin or foreign substance which induces an immune response) either from a pathogen or vaccination.3
Below is an excellent video from TedEd that provides a simple yet detailed explanation of how the immune system works.
Types of vaccines
There are several different types of vaccines that use various mechanisms to ‘teach’ our immune systems how to fight off specific pathogens. These are:
Inactivated vaccines use a version of the pathogen that has been killed. These vaccines generally require several doses or boosters for immunity to be ongoing. Examples include Flu, Hepatitis A and Polio.
A live-attenuated vaccine uses a weakened live version of the pathogen, mimicking natural infection without causing serious disease. Examples include Measles, Mumps, Rubella, and Chickenpox.
Messenger RNA (mRNA) vaccines
An mRNA vaccine contains no actual part of the pathogen (alive or dead). This new type of vaccine works by teaching our cells how to make a protein that will in turn, trigger an immune response. In the context of Covid-19 (the only mRNA vaccine approved for use in the form of the Pfizer and Moderna vaccinations), the vaccine instructs our cells in making a protein found on the surface of the Covid-19 virus (the spike protein). This causes our bodies to create antibodies. After delivering the instructions, the mRNA is immediately broken down.4
Subunit, recombinant, polysaccharide, and conjugate vaccines
Subunit, recombinant, polysaccharide, and conjugate vaccines do not contain any whole bacteria or viruses. These vaccines use a piece from the pathogen’s surface —like its protein, to elicit a focused immune response. Examples include Hib (Haemophilus influenzae type b), Hepatitis B, HPV (Human papillomavirus), Whooping cough (part of the DTaP combined vaccine), Pneumococcal and Meningococcal disease.5
Toxoid vaccines are used to protect against pathogens that cause the release of toxins. In these cases, it is the toxins that we need to be protected from. Toxoid vaccines use an inactivated (dead) version of the toxin produced by the pathogen to trigger an immune response. Examples include Tetanus and Diphtheria.6
A viral vector vaccine uses a modified version of a different virus (the vector) to deliver information in the form of a genetic code from a pathogen to our cells. In the case of the AstraZeneca and Janssen/Johnson & Johnson vaccines and Covid-19, for example, this code teaches the body to make copies of the spike proteins – so if exposure to the actual virus occurs, the body will recognise it and know how to fight it off.7
The video below was developed by Typhoidland and The Vaccine Knowledge Project and describes what happens inside our cells when we are infected with a virus – using Covid-19 as the example.
- Science Learning Hub. (2010). The body’s first line of defence. Available: https://www.sciencelearn.org.nz/resources/177-the-body-s-first-line-of-defence Last accessed 18 Nov 2021.
- Khan Academy. (Unknown). Innate Immunity. Available: https://www.khanacademy.org/test-prep/mcat/organ-systems/the-immune-system/a/innate-immunity Last accessed 18 Nov 2021.
- Molnar, C., & Gair, J. (2015). Concepts of Biology – 1st Canadian Edition. BCcampus. Retrieved from https://opentextbc.ca/biology/
- Mayo Clinic Staff. (Nov 2021). Different types of COVID-19 vaccines: How they work. Available: https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/different-types-of-covid-19-vaccines/art-20506465 Last accessed 19 Nov 2021.
- Office of Infectious Disease and HIV/AIDS Policy (OIDP). (2021). Vaccine Types. Available: https://www.hhs.gov/immunization/basics/types/index.html Last accessed 16 Nov 2021.
- Vaccine Knowledge Project. (2021). Types of vaccine. Available: https://vk.ovg.ox.ac.uk/vk/types-of-vaccine Last accessed 17 Nov 2021.
- CDC. (Oct 2021). Understanding Viral Vector COVID-19 Vaccines. Available: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines/viralvector.html#:~:text=First%2C%20COVID%2D19%20viral%20vector,is%20called%20a%20spike%20protein Last accessed 19 Nov 2021.