COVID-19 Vaccines

COVID-19 Vaccines

Both Pfizer and Moderna report that their vaccines show approximately 95% efficacy at preventing both mild and severe symptoms of COVID-19 after two doses.

Pfizer claims their late-stage trials found its vaccine was about 52% effective after the first dose, with study results showing protection starting as early as 12 days after receiving it. A week after the second dose (given after 21 days from the first dose), the shot’s effectiveness rose to 95%.

Ideally we should receive the vaccine dosing schedules ‘as recommended’ by the manufacturer because data has not yet formally supported that any delays in getting a second shot will offer the same effective immune response.

Once vaccinated, we will need to continue to wear our masks as research is still pending to show if the vaccine will PREVENT ASYMTOMATIC SPREAD.

Vaccines in Canada

Currently approved vaccines in Canada are Pfizer, Moderna, and AstraZeneca.

Pending approval vaccines in Canada are Johnson & Johnson and Sanofi.

Pathway to Immunity

The goal of widespread vaccination for the coronavirus means that the virus will not infect as many people once we achieve a critical percentage of the population vaccinated. Presently this number ranges from 65-80% depending on the number of active cases in one community. This will limit spread through communities.

Immunity is irrelevant if new COVID-19 strains are resistant to the vaccines now used. 

We need to urgently get the world vaccinated to slow down spread of the virus and its opportunity to continually mutate with new hosts. It will take about 3 months of production time to modify the mRNA vaccines to cope with new DNA mutations. And yes, another round of vaccinations around the world will be required.

Source: A model created by Professor Troy Day of how the new coronavirus variant could spread in Ontario. (Ontario Science Advisory and Modelling Consensus Tables.)

Dr. Day states: “The threat posed by the more contagious variant partly lies in the time it takes for the number of COVID-19 cases to double, between 10 and 15 days, far fewer than the estimated 40 days of the current coronavirus strain.”

Dr. Troy Day, member of the Ontario Modelling Consensus Table, mathematical biology at Queen’s University in Kingston.

The Newer Virus Strains

Globally, the UK strain known as B.1.1.7, has now shown up in more than 50 countries. Though this strain is no more deadly than the present dominant stain, a more contagious strain could be worse because it makes people sicker and because so many more people become infected, resulting in a higher death toll.

After about a month, a 50% more deadly strain would cause 1.5 times the number of deaths compared to baseline. But a 50% more contagious strain could cause over 11 times the number of deaths over the same time period. That’s if you assume an average of five days from the time someone gets infected, and the time they infect someone else.

More Contagious = More Cases = More Hospitalizations = More DEATHS

Other variants, identified in South Africa (B.1.351) and Brazil (P.1 and P.2), haven’t traveled as far and wide, but show a different range of mutations.

So far, none of the newer strains have mutated to the point that it causes more severe disease, or evades the protection provided by vaccination. While some of the new variants appear to have changes that look like they could affect immune response, it’s only by a matter of degree.

Duration of Immunity

The duration of vaccine immunity is currently unknown. Moderna is suggesting approximately 1 year. To check for continued presence of antibodies will require a blood test.


COVID-19 Question Guide

Herd immunity is when a high proportion of individuals are resistant to the spread of the virus due to vaccination. The level of herd immunity needed can vary from disease to disease however for COVID-19 we will require at least an 80% vaccination rate. If the pandemic worsens that rate could increase.

mRNA vaccines are like CD players that can play any kind of CD – classical music, rap or pop. The scientists had the CD player before COVID-19 hit due to previous research being done on mRNA technology. Once they figured out the Coronavirus CD, they could place it into the player and make the vaccine a lot faster than before, since they used what was known and built on it.

Canada government website: Canada is rolling out the vaccine based on priority populations.

First group:

  • residents and staff of shared living settings who provide care for seniors
  • adults 70 years of age and older, with order of priority:
    • beginning with adults 80 years of age and older
    • decreasing the age limit by 5-year increments to age 70 years as supply becomes available
  • healthcare workers who have direct contact with patients, including:
    • those who work in health care settings
    • personal support workers
  • adults in Indigenous communities


  • healthcare workers not included in the initial rollout
  • residents and staff of all other shared living settings, such as:
    • homeless shelters
    • correctional facilities
    • housing for migrant workers
  • essential workers who face additional risks to maintain services for the functioning of society

Depending on the province or territory you live in the roll-out schedule could differ. You can find your provinces roll out schedule here.

Both Pfizer and Moderna have released their ingredient lists, which can be found online. Neither vaccine contains mercury, formaldehyde, aluminum, or fetal cells.

Pfizer-BioNTech COVID-19 vaccine

Moderna COVID-19 vaccine

Depending on which vaccine the answer varies.

Both the Moderna and Pfizer series requires at least two vaccines.

According to a document submitted to the FDA, the Moderna vaccine can provide 50.8% efficacy of the first dose on days 1-14 and then 92.1% post 14 days for an overall 80.2% protection after one dose compared to 95% after the second dose 28 days apart.

The Pfizer vaccine after one dose was shown to have an efficacy of 52% verses the above 90% after two doses 21 days apart.

It is unknown whether the immunity from a single vaccine would continue or drop off as no research was done to study this. Both briefing documents submitted to the FDA state that the available data “cannot support a conclusion on the efficacy of a single dose of the vaccine”.

The Janssen (Johnson & Johnson) vaccine that released their Phase three clinical trial results shows an overall efficacy of 85% against severe disease and 66% after moderate to severe disease, 28 days after vaccination.

There is little to say about extending the interval between doses as the trials conducted did not test for the extended interval time, we just don’t know how the efficacy of a vaccine continues past a certain stage. We will all be looking at the UK to see how this extension has affected their vaccination efficacy as they are one of the first to administer this new schedule.

No clinical trials have been done by Moderna or Pfizer to look at how long immunogenicity lasts following one does. All Pfizer vaccine trial participants received the second dose 21 days after their first, Pfizer has stressed that there is no evidence of efficacy for the first dose after 21 days. (Mahase, 2020)

Based on unpublished data available to the National Advisory Committee on Immunization through Health Canada for both the Pfizer-BioNTech and Moderna vaccines, there was no difference in vaccine efficacy between the people who got their second dose at day 19 and the people who got it at day 42. (Tauh, Mozel, Meyler, & Lee, 2021)

It is recommended by the Government of Canada to follow the original dosing schedules however due to logistical constraints it may not be possible. (Tauh, Mozel, Meyler, & Lee, 2021)

There is no evidence on the interchangeability of the COVID-19 vaccines. Studies are currently under way, but no results have yet been released.

Carter, A. (2021, Jan 20). Debunking myths: Ontario doctors explain why most people should get COVID-19 vaccines. Retrieved from CBC:

Centre for Effective Practice. (2020). Answering questions about COVID-19 vaccines: a guide for healthcare providers. Centre for Effective Practice.

Cleveland Clinic. (2020, Dec 23). 9 Common COVID-19 Vaccine Myths Explained. Retrieved from Cleveland Clinic:

FDA. (2020). Vaccine and related Biological Products Advisory Commitee: Pfizer-Biontech COVID-19 Vaccine (BNT162, PF-07302048). Pfizer.

FDA. (2020). Vaccines and Related Biological Products Advisory Committee Meeting: FDA Briefing Document Moderna COVID-19 Vaccine. ModernaTX, Inc.

Henry Ford Health System Staff. (2020, Dec 21). 10 Myths About The COVID-19 Vaccine That Aren’t True. Retrieved from Henry Ford Health System:

Iacobucci Gareth, M. E. (2021). Covid-19 vaccination: What’s the evidence for extending the dosing interval? The BMJ .

Mahase, E. (2020). Covid-19: Pfizer vaccine efficacy was 52% after first dose and 95% after second dose, paper shows. The BMJ.

Moore, J. P. (2021). How do you take your vaccine—one lump or two? BMJ Opinion.

Tanula, M. (2020, Dec 9). COVID-19 vaccine myths debunked. Retrieved from Mayo Clinic:

Tauh, T., Mozel, M., Meyler, P., & Lee, S. M. (2021). COVID-19 VACCINE DOSING SCHEDULE – WHAT IS THE EVIDENCE? BC Medical Journal.

Learn More About the Vaccines

Vaccine Biology 101

Traditional vaccines
vs mRNA vaccines


Side Effects

Precautions and adverse reactions


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