How do vaccines work?

Vaccines are used to help protect people from diseases, reducing their risk of serious illness and/or death in some cases.  They do this by helping your immune system. Your body’s immune system is designed to fight off invaders, like viruses. Often the sickness you feel when your sick is your body at work fighting off the disease. Once your body’s immune system has fought off a virus, it remembers that particular virus and knows how to find and destroy it before it causes the disease again. This is called immunity.

A vaccine protects against disease by helping your immune system create antigens – these are parts of organisms designed specifically to fight a virus/disease, helping the immune system prepare a good response before the actual disease is present. This means you don’t have to get the disease for your body to be prepared to fight it.

COVID-19 vaccines fall into two types [1].

mRNA vaccines

mRNA vaccines provide instructions to your cells for how to make a coronavirus protein antigen. Once your cells have made the coronavirus protein, this protein will trigger a response from your immune system that will help to protect you against COVID-19.

Think of it like building a piece of furniture from a kit. The company provides you with the instructions and the materials you need to build the furniture. An mRNA vaccine works the same way.

Pfizer and Moderna brand COVID-19 vaccines are examples of mRNA vaccines. If you would like to see a visual representation of how an mRNA vaccine works, view this infographic from the University of Waterloo | School of Pharmacy.

You can also watch this Health Canada video on mRNA vaccines.

Viral vector vaccines

Viral vector vaccines supply ready-to-use antigens to produce coronavirus proteins in your body without causing disease. Just like mRNA vaccines, these antigens will trigger a response from your immune system.

Remember, antigens fight disease: pathogens carry the disease.

No matter what kind of vaccine you get, it gives you a much higher level of protection from life-threatening disease.

How vaccines protect you & your community

The more people who get vaccinated, the harder it is for the COVID-19 disease to infect you and your community. Think of it like a protective wall – the disease has a harder time getting through.

There are some people who unfortunately can’t get vaccinated because of health conditions or allergies. But your vaccination can also protect them, because it means it is less likely for you to get the disease. And if everyone in that person’s life gets vaccinated, they have a much higher chance of not getting the disease.

More information

We have more resources on COVID-19 vaccines, including how to access them and answers to frequently asked questions.

[1] How do vaccines work? | The World Health Organization