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Updated COVID-19 Vaccine Information

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Updated June 9, 2021

The Peterborough FHT COVID-19 Vaccine Pilot Project

TOPIC: Planning for Second Doses of COVID-19 Vaccines


As many of you are aware, NACI (Canada’s vaccine advisory panel) released updated recommendations on Tuesday, June 1 2021 which are relevant to you as they give you a CHOICE as to what COVID-19 vaccine you receive for your SECOND DOSE. The NACI statement is attached below for your reference.

As of today, you essentially have TWO choices:
1) A second dose of AstraZeneca vaccine, administered at least 12 weeks after your initial dose of AZ
2) A second dose of an mRNA vaccine (the current ones in use being the Pfizer-BioNTech and Moderna vaccines), also administered at 12 weeks after your initial dose of AZ.

Purpose of this Communication:
To give you more information about your choices and to help you make an informed decision based on the most current information available.


A Second Dose of AstraZeneca

  • Rationale:
  • The majority of existing medical evidence on current COVID-19 vaccines is generally based on studies of 2 doses of the same vaccine. This evidence has established the efficacy and safety data that is often quoted by health care providers. This data continues to evolve with real-world use of the vaccines.

  • Timing:
    • The second dose of AstraZeneca should be given at least 12 weeks after the first dose, as this seems to provide a much better immune response than after shorter dose intervals.
  • Benefits (after a 2 dose series):
    • Protection from severe illness and hospitalization: 100%
    • AstraZeneca seems to offer some specific protection against the B.117 variant, which is currently the predominant strain circulating in Ontario.
  • Risks:
    • • VITT Risk:
      • • AstraZeneca is no longer being used for FIRST DOSE in Canada due to the risk of VITT (Vaccine-induced Thrombosis and Thrombocytopenia) - ie “blood clots”.
      • • At the time of your first vaccinations, this risk was believed to be around 1 in 1million cases.
    • • As of May 7th, the Ontario COVID-19 Science Advisory Table estimates this risk to be around 1:55,000 which, although still very low, is considerably higher than first believed as more information has come forward.
  • • The risk of VITT following a SECOND DOSE of AstraZeneca is believed to be LOWER, around 1:600,000
    • • It is important to remember that this number can also change (higher or lower) as more information is learned
  • • An important consideration is that although VITT is RARE, it is also SERIOUS - the case fatality rate (ie chances of dying) or risk of serious outcomes if VITT is diagnosed is high
    • • NACI estimates the case fatality rate at 25-40%, although this may decrease over time with increased awareness

A Second Dose of Pfizer or Moderna:

  • Rationale:
    • “Mixing and matching” of COVID-19 vaccines is believed to offer several advantages, including the development of different types of antibodies which theoretically boosts the immune system. NACI claims that preliminary evidence suggests this is the case with this approach.
    • We have lots of experience mixing vaccines as part of Ontario’s Immunization Program - for illnesses like influenza, hepatitis A and others - so the concept is not new.
  • Timing:
    • Ontario announced on June 3rd that people who received a first dose of AstraZeneca will be eligible to book their second dose with an mRNA vaccine using the provincial booking system starting the week of June 7th
  • Benefits:
    • The efficacy data of a second dose of an mRNA vaccine following a first dose of AstraZeneca is currently under study.
      • According to the Public Health Agency of Canada, the Spanish study found those who had an initial dose of AstraZeneca vaccine and got a second shot of Pfizer had an increase in antibodies that were 30 to 40 times higher than in a control group who only received one AstraZeneca dose.
  • Safety:
    • Preliminary data from studies in Germany and Spain suggests that this combination is SAFE.
    • Pfizer and Moderna have NOT been associated with a risk of VITT.
  • Risks:
    • There is a possibility of increased short-term side effects when using mixed COVID-19 vaccine schedules, including headache, fatigue and feeling generally ill (NACI).
      • • They are more likely with a shorter dose interval (ie 4 weeks).
        • • In Ontario, this interval will obviously be longer than this as >8 weeks have already passed since your first doses.
      • • These side effects are MILD, and NOT-SEVERE, and resolve with time and without complication.
    • Several studies on the efficacy of this “mix and match” approach are ongoing, including a larger one in the United Kingdom.
      • We do not yet have the final data from these studies to review.
      • More information is expected later this month.

    How to Book a Second Doses:

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