This is a summary, written by members of the CITF Secretariat, of the five presentations given at the CITF Scientific Meeting in Vancouver, March 8-10, 2023, during the breakout session entitled, Vaccine safety and effectiveness.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

CITF-funded studies show the important role that vaccines have played in protecting Canadians and people worldwide from severe COVID-19. Here, we summarize results from the five presentations given during the breakout session “Vaccine safety and effectiveness” at the CITF Scientific Meeting in Vancouver, March 8-10, 2023. Some study teams presented vaccine safety through the identification of potential side effects, while others addressed vaccine efficacy and the protection conferred by subsequent doses, including the bivalent booster vaccines.

1. Presenter Dr. Phyumar Soe and CITF PI Dr. Julie Bettinger: COVID-19 vaccine safety among older adults aged 65 and above: A Canadian Immunization Research Network (CIRN) study

This study’s objective was to determine the frequency of health events (whether common and uncommon) occurring within seven days of a first or second COVID-19 vaccine dose in adults aged 65 and above.

  • Among older adults, those who received either one or two doses of the AstraZeneca or the mRNA-1273 vaccine (Moderna) had a high likelihood of health events that caused work absenteeism, prevented daily activities, and/or required medical care in the first week following vaccination. The health events were self-limiting and were not associated with emergency visits or hospitalization.
  • The common symptoms following vaccination with AstraZeneca and Moderna included feeling unwell, fever, headache, gastrointestinal symptoms, and arthritis.

2. Presenter Dr. Ramandip Grewal and CITF PI Dr. Jeffrey Kwong: Effectiveness of mRNA COVID-19 monovalent and bivalent vaccine booster doses against Omicron severe outcomes among adults aged ≥50 years in Ontario, Canada: A Canadian Immunization Research Network (CIRN) study

This study estimated the effectiveness of monovalent and bivalent mRNA COVID-19 vaccine booster doses against severe outcomes due to Omicron. Researchers focused on community-dwelling adults aged 50 years and older.

  • The monovalent and bivalent mRNA COVID-19 vaccines provided similar short-term protection: up to four months against severe outcomes (hospitalization and death).
  • Vaccine effectiveness against severe outcomes was slightly lower during the SARS-CoV-2 BQ predominant period compared to the previous BA.4/BA.5 predominant period.

3. Presenter Dr. Kyla Hildebrand and CITF PI Dr. Karina Top: Revaccination outcomes among individuals aged 12+ with suspected hypersensitivity reactions following SARS-CoV-2 vaccination: A Canadian Special Immunization Clinic (SIC) Network study

This presentation described a national cohort of patients at risk of, or referred for, suspected hypersensitivity reactions following COVID-19 vaccination. The goal was to determine the risk, on being revaccinated, of a recurrence of an adverse event following immunization (AEFI) and identify risk factors associated with AEFI recurrence.

  • 84% of patients seen for allergy-like AEFIs were safely revaccinated after allergist assessment.
  • Patients with a history of allergic reactions to vaccines did not experience type I hypersensitivity (an abnormal immune response triggered by exposure to specific antigens known as allergens) to COVID-19 vaccines.

4. Presenter Gabrielle Gaultier and CITF PI Dr. Agatha Jassem: Immunogenicity of COVID-19 vaccine four-dose series in healthy community dwelling adults 50 years and above in Canada: Interim analysis from the ‘PRospEctiVe EvaluatioN of immuniTy after COVID-19 vaccines’ (PREVENT-COVID) study

This study aimed to establish the immunogenicity of COVID-19 vaccines in community-dwelling adults over 50 years old.

  • COVID-19 mRNA vaccine boosters maintained similar concentrations of SARS-CoV-2 anti-spike protein IgG when compared to pre-booster levels.
  • The combination of mRNA/mRNA/mRNA vaccine and the AstraZeneca vaccine resulted in similar concentrations of anti-spike protein IgG and higher concentrations of anti-spike IgG than the AstraZeneca/mRNA/mRNA combination.
  • mRNA boosters maintained anti-spike protein IgG avidity (strength with which IgG binds to antigenic epitopes expressed by a given protein, in this case spike protein).

5. Presenter Dr. Victoria Kirsh and CITF PI Dr. Philip Awadalla: Real-world COVID-19 vaccine effectiveness: an analysis from the ‘SUrveying Prospective Population cOhorts for COVID-19 prevalence and outcomes in Canada’ (SUPPORT-Canada) study

This study measured vaccine effectiveness in a real-world setting over the course of the pandemic. The goal was to determine the relationship between vaccination status and one’s risk of a new SARS-CoV-2 infection. The team controlled for base infection rates that may have varied at the time of follow-up and by geographic region, as well as by participant demographics and adherence with public health recommendations.

  • Overall, vaccines were effective at stopping SARS-CoV-2 infection pre-Omicron.
  • Overall, full or booster vaccines prevented SARS-CoV-2 Omicron infections for a short period. Evidence of waning immunity was shown as a high of 56-68% at one/two months post dose dropped to a low of 3-30% at five months or longer after vaccination.
  • The highest vaccine effectiveness was among Moderna vaccine recipients, with bivalent boosters having a similar effect to monovalent boosters.
  • An increase in anti-sterol methyltransferase 1 (SmT1)It’s involved in controlling levels of cholesterol and is a marker of vaccination in this study. and anti-receptor binding domain (RBD) antibody levels was associated with a decreased risk of SARS-CoV-2 infection during the Omicron predominant period.