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How Getting Vaccinated Protects Those Who Can't

The Pfizer vaccine has recently been distributed for use across North America, approved by both the Food and Drug Administration (FDA) in the United States, and Health Canada in Canada.

A suggestion issued on Saturday, December by the Government of Canada suggests that individuals allergic to ingredients in the vaccine should not take the vaccine. This much seems obvious, but how will those individuals protect themselves from COVID-19? What about other individuals such as children under 16 (who the vaccine has not been approved for yet), individuals with underlying health conditions, or pregnant individuals (amongst hundreds of other scenarios) who should not get vaccinated?

This is where healthy individuals enter the picture. Some people assume that because they are healthy, they do not have to get vaccinated because they are at lower risk, but it’s actually because they are healthy that they should get vaccinated.

When an individual gets vaccinated, they are not only protecting themselves and their family; they are actually protecting their entire community. This is called herd immunity.

Herd immunity (also known as “population immunity”) is a principle in immunity that when a certain percentage of the population has been vaccinated (a vaccination “threshold” is reached), the entire population then becomes protected.

Herd immunity is achieved by protecting people from a virus, not by exposing them to it.

- World Health Organization

It is still completely uncertain what this “percentage” is for COVID-19. The percentage can also fluctuate based on a variety of factors (housing, population density, etc) in communities. This is why it is important that as many people get vaccinated as possible; there should not be a “target” the population should be trying to reach.

In simple terms, vaccinations work by activating the cells of the immune system. By injecting a small, non-fatal amount of the virus into the body, an immune response is triggered. B-lymphocytes and T-lymphocytes (disease fighting white blood cells) can take a long time to become abundant the first time they encounter a disease, but once they have fought it off once, they tend to remember. The purpose of vaccinations is to develop this memory without harming the body! These special cells are called “memory cells” and allow for the body, in case it comes in contact with the disease again, to quickly concentrate its resources to kill it before the person experiences severe symptoms or transmits it.

With the new COVID-19 vaccines rolling out, the hope is that as much of the population has this cellular memory as possible.

Some examples of herd immunity in action in the past include the rarity of measles, mumps, and polio. In the United States, these diseases used to be extremely abundant, but with the help of vaccines, have since become less severe and common. Even though a certain part of the population (CDC on who should not get vaccinated) is not able to get the vaccine, they are protected by those who can!

These diseases are also perfect examples of what can happen without herd immunity. Communities (schools, neighbourhoods, etc.) that have “less vaccine coverage”—either because of socio-economic or educational factors—will experience many more outbreaks than those that have a higher coverage. These communities are the ones without herd immunity.

Be sure to play a role in protecting your community when you get the choice (and if you are able to) because it works! Every single person counts.


Centers for Disease Control and Prevention. (2018, July). Understanding How Vaccines Work.

Retrieved December 12, 2020, from

Dowdy, D., & D'Souza, G. (2020, April 10). What is Herd Immunity and How Can We Achieve It

With COVID-19? Retrieved December 12, 2020, from

World Health Organization. (2020, October 15). Coronavirus disease (COVID-19): Herd

immunity, lockdowns and COVID-19. Retrieved December 12, 2020, from https://www

Featured image is courtesy of via Pexels.

Article Author: Linda Duong

Article Editors: Victoria Huang, Valerie Shirobokov


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