In a recent newsletter released on their website, CITF-funded researcher Dr. Prabhat Jha and his Action to beat Coronavirus (Ab-C Study) team report findings on the third phase of their study covering data up until October 2021, prior to the Omicron wave. The researchers acknowledge that lack of testing across Canada likely results in under-estimating the rate of infection. Preliminary Ab-C data from early February, during the Omicron wave, shows that 9% of participants reported testing positive in January 2022 with another 5% potentially infected based on symptoms.
Beginning in 2020, the Ab-C study team recruited a nationally representative sample of 14,621 Canadians. Participants were asked to complete a series of online surveys conducted by Angus Reid, an established online public opinion community. This newsletter provides findings from Ab-C Phase 3 which ended in October 2021. A sub-study of 4,438 participants completed a dried blood spot (DBS) test and were asked about their COVID-19 infection history and vaccine status. Participants were grouped into five categories: 1) Immune-naïve (no infection history or vaccination), 2) infection only, 3) one vaccine dose and uninfected, 4) two vaccine doses and uninfected, 5) two vaccine doses and infected.
- 95% of participants had been vaccinated, and most had at least two doses.
- The most common source of immunity as of October 2021 was two vaccine doses, with older Canadians more likely to be fully vaccinated than younger people.
- Less than 1% of participants had had a third dose of vaccine by October.
- Pre-Omicron, there were few COVID-19 infections among those aged 18-39. In the 40-59 age group, which has the highest proportion of participants with COVID-19 infection history, less than 10% had been infected.
- Considering both infection history and vaccination together, those aged 40-59 had the highest proportion (5%) without any immunity (i.e. “immune-naïve”).
- Preliminary data from early February, during the Omicron wave, shows that 9% of participants reported testing positive in January 2022 with another 5% potentially infected based on disclosure of symptoms.
Dr. Jha and his team suggest that the lack of testing availability during the Omicron wave resulted in reported infection rates that likely underestimate the true number of COVID-19 infections across Canada. Their analyses is ongoing to investigate this.