Stephanie Hwang
- Oct 16, 2021
- 5 min read

COVID Vaccines: Side-by-Side

Edited by Olivia McPherson

The 2019 coronavirus disease (COVID-19) is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Common symptoms of COVID are fever, chills, difficulty breathing, and loss of taste or smell. In severe cases, it can lead to hospitalization or death.

Despite its contagious nature, the number of cases throughout the world are plateauing, largely due to the rise of COVID vaccines. Vaccines stimulate the production of antibodies and build immunity against certain diseases without getting ill. There are a number of vaccines that are being administered throughout the world: Pfizer-BioNTech, Moderna, Oxford-AstraZeneca, and Johnson & Johnson.

So, what are the key differences between the COVID vaccines?

Pfizer-BioNTech (Comirnaty)

On December 9, 2020, Health Canada authorized the use of the Pfizer vaccine under the Interim Order Respecting Importation, Sale and Advertising of Drugs for Use in Relation to COVID-19. On May 5, 2021, authorization to use this vaccine expanded to include those aged 12 to 15.

Type: mRNA (virus genetic code)

Antigen: Spike protein, 30 μg

Doses: Two injections, 21 days apart

Preparation: Dilute with 1.8 mL 0.9% sodium chloride

Doses per vial: 6 doses (0.3 mL/dose)

Recommended for: 12 years old and older

Administration Route: Intramuscular (IM)

Most vaccines work by introducing the body to a weakened or inactivated disease germ. However, the Pfizer vaccine works differently. This vaccine delivers a specific piece of genetic coding from the SARS CoV-2 virus that contains “blueprints” for making spike proteins. Typically, spike proteins are responsible for penetrating and infecting host cells. By exposing the immune system to the spike protein, the body is able to produce antibodies and develop memory cells to quickly recognize and respond if the body is infected with the actual virus.

This vaccine is approximately 95% effective against hospitalization with COVID-19 in those without prior infection. Immunity tends to start 28 days after the first dose (or 7 days after the second dose). It may help prevent COVID-19 regardless of age, gender, race, ethnicity, BMI, or present co-morbidities. Healthcare providers are recommended to observe the patient for at least 15 minutes after vaccine administration in case of an emergency. If someone has a history of a severe reaction to a vaccine (such as anaphylaxis), they are recommended to stay under observation for at least 30 minutes.

The greatest challenge with this vaccine is storage and stability. When first introduced, it required storage in ultra-cold temperatures at -70˚C (-94˚F) for longer stability. With further research on the vaccine’s stability, Pfizer has now released guidance on safely storing vials at more typical refrigerator and freezer temperatures, which has improved accessibility to this vaccine, especially in community pharmacies.

Moderna (Spikevax)

The Moderna vaccine was the second approved vaccine to prevent COVID-19. Use of this vaccine was authorized by Health Canada on December 23, 2020 under the Interim Order Respecting the Importation, Sale and Advertising of Drugs for Use in Relation to COVID-19.

Type: mRNA (virus genetic code)

Antigen: Spike protein, 100 μg

Doses: Two injections, 28 days apart

Preparation: No preparation needed

Doses per vial: 10-15 doses (0.5 mL/dose) [depending on vial size]

Recommended for: 18 years and older

Administration Route: Intramuscular (IM)

Similar to the Pfizer vaccine, the Moderna vaccine uses mRNA to introduce the body to SARS CoV-2 spike protein. The vaccine teaches our immune system to recognize the foreign spike protein and produce antibodies to fight COVID-19. In this way, the body can trigger an immune response without being exposed to the live virus.

This vaccine is about 95% effective against hospitalization with COVID-19, as documented at 14 days after the second dose. After vaccine administration, healthcare providers are recommended to observe the patient for at least 15 minutes in case of an emergency. If someone has a history of a severe reaction to a vaccine (such as anaphylaxis), they are recommended to stay under observation for at least 30 minutes.

The Moderna vaccine is slightly more stable than the Pfizer vaccine. It can be shipped and stored long-term if kept in normal freezer conditions and up to 30 days in standard refrigeration.

AstraZeneca (Vaxzevria)

The AstraZeneca vaccine has two distinct benefits when compared to the other COVID-19 vaccines. First, it is cheaper to produce per dose, and second, it can be stored, transported, and handled in standard refrigeration for at least six months. This vaccine was temporarily pulled off the market in March 2021 due to concerns of blood clots. This was a very rare side effect that occurred within two weeks after vaccine administration. However, it was decided that, with an unreliable supply of Moderna and Pfizer vaccines, the benefits of the AstraZeneca vaccine outweighed its risk of very rare blood clots.

Type: Protein adjuvant

Doses: Two injections, 4 to 12 weeks apart

Preparation: No preparation needed

Doses per vial: 8-10 doses (0.5 mL/dose) [depending on vial size]

Recommended for: 18 years old and older

Administration Route: Intramuscular (IM)

This vaccine was authorized for use by Health Canada on Februrary 26, 2021 and works by exposing the body to a modified version of the adenovirus. Of note, the carrier vaccine does not contain the virus that causes COVID-19. Instead, it produces a spike protein. This causes the body’s immune system to respond with the creation of antibodies and memory cells to fight against the live virus. Based on clinical trials, it is 62% effective against COVID-19 at least 15 days after the second dose.

In May 2021, administration of AstraZeneca as a first dose was halted out of an abundance of caution and due to an increased supply of mRNA vaccines. Those who had already received AstraZeneca as their first dose have the freedom to choose either AstraZeneca OR an mRNA vaccine as their second dose, both of which are completely acceptable.

Johnson & Johnson (Janssen)

On March 5, 2021, Health Canada authorized the use of this vaccine under the Interim Order Respecting Importation, Sale and Advertising of Drugs for Use in Relation to COVID-19. This vaccine can be stored, transported, and handled at normal refrigeration and only requires one dose for full efficacy. These characteristics make the Janssen vaccine easier to distribute and administer in the community.

Type: Recombinant adenovirus (Ad26) vector

Antigen: Spike protein, 5x1010 viral particles

Doses: Single dose

Preparation: No preparation needed

Doses per vial: 5 doses (0.5 mL/dose)

Recommended for: 18 years old and older

Administration Route: Intramuscular (IM)

This vaccine is approximately 77% effective at preventing severe or critical cases at 14 days. It is 85% effective at 28 days after administration.

Of note, this vaccine was temporarily pulled from market in the US due to concerns about the increased risk of blood clots. In extremely rare instances, six women aged 18 to 48 experienced a blood clot approximately six to thirteen days after receiving the vaccine. However, the incidence of blood clots post-vaccine administration is less than the average incidence of blood clots in the general population. Therefore, it was determined that the benefits of the vaccine outweigh the risks of blood clots.

Although this vaccine has been approved, there is no supply of it currently in Canada.

Takeaways

Ultimately, some immunity provided by any vaccine is better than no immunity. Vaccines are the most effective way to protect yourself, your family and friends, and your community against COVID-19. Each vaccine dose administered is one step closer to herd immunity and returning to a normal world.

Vaccines are publicly funded and available to everyone in Canada, including those who are not citizens. Find out how to get vaccinated near you: https://www.canada.ca/en/public-health/services/diseases/coronavirus-disease-covid-19/vaccines/how-vaccinated.html#a1

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