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March 9, 2021 • read

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The COVID-19 vaccine and herd immunity

COVID-19 vaccines will be given out across Canada in the coming months. The vaccine will help Canada reach something called herd immunity — a common ending to viral outbreaks. Here’s what herd immunity is, how it works, and how long it might take us to achieve it.

What is herd immunity?

Herd immunity is a type of indirect protection from a contagious disease. When enough people in a community are immune to a disease, it’s harder for that disease to spread. Once the disease can’t find any more hosts, it dies out altogether.

Herd immunity protects people who can’t get the COVID-19 vaccine for health reasons. If enough healthy people get the vaccine, the overall rate of new infections will decrease. Then, medically vulnerable people have less of a chance of being exposed to the virus.

How many people need to be immune before we reach herd immunity?

Each infectious disease has a threshold, which is the number of infected people required for a disease to spread at high rates. For a population to have herd immunity, the number of people who are immune has to be equal to or above the threshold. 

The threshold for herd immunity is different with every disease. In the case of measles, another infectious illness, it took 95% of the population being vaccinated to stop the spread. That differed from polio, where only 80% of a community needed to be vaccinated to snuff out new infections. Since COVID-19 is a new coronavirus, scientists are still learning its threshold for herd immunity.

How does herd immunity happen?

Herd immunity is achieved either by large numbers of a population catching the disease and recovering from it, or through mass vaccination. 

Becoming infected

When a harmful foreign substance like a virus or bacteria enters your body, your immune system creates antibodies. Antibodies are proteins that your immune system uses to identify, attack, and destroy the disease. Over time, the more your body is exposed to the unwanted germ, the better it gets at identifying and destroying it. Eventually your immune system is able to attack and destroy the intruder so quickly that you don’t develop any symptoms. This is called immunity. 

With COVID-19, people who have caught it and recovered now have COVID-19 antibodies in their systems. However, there’s still a lot we don’t know about the strength or duration of protection. The number of antibodies a person develops can vary. For example, someone who caught COVID-19 and developed symptoms might have more antibodies in their system than someone who was asymptomatic. We can’t be sure that everyone who contracted COVID-19 has developed enough antibodies to become immune. Scientists are still discovering the level of antibodies needed for immunity and how long those antibodies last.


Vaccines contain a small part of a virus, bacteria, or disease-causing organism that’s either dead or weakened. With the COVID-19 vaccine, a small amount of the virus is introduced to your system in a controlled way. It’s not strong enough to cause you to become infected. Instead, your immune system learns how to identify the virus and develop antibodies. If you’re exposed to the COVID-19 virus in the future, your immune system will know how to destroy it before it makes you sick and contagious. 

Once enough people get the COVID-19 vaccine, the number of new cases will start to decline. Once they’re so low that becoming infected is unlikely, we can look forward to taking small steps back towards our normal social habits.

How long will it take for us to develop herd immunity?

When it comes to how quickly we can reach herd immunity, there are a lot of moving parts to consider. 

Vaccine rollout

Not everyone can be vaccinated at once. Vaccine rollout will depend on vaccine availability, and will prioritize the most medically vulnerable first. 

Keeping new infection rates low

If infection rates continue to rise, it will take us longer to reach an adequate threshold of people who are immune and healthy. The fewer new cases of COVID-19 there are week to week, the faster we reach the threshold.

How many people get vaccinated

There will need to be a significant amount of Canadians willing to be vaccinated. The exact number is still unknown.

New strains of COVID-19

Several new strains of COVID-19 have been detected around the world. This isn’t unusual — viruses normally mutate. So far there isn’t cause for alarm. However the more people there are who have immunity, the less chance the virus has to mutate in unpredictable ways as it passes from one person to the next. 

The best way to help your community achieve herd immunity is by following public health guidelines. Make social distancing, mask wearing, and hand-washing part of your daily routine wherever possible. The fewer new cases there are in Canada while the vaccine is rolling out, the faster we’ll get to enjoy the benefits of herd immunity.

COVID-19 has been tough on all of us, mentally and physically. Speak to one of our doctors or therapists to get help for your individual needs. 

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