Ab-C Newsletter (December 2021)

Welcome to the sixth edition of the Ab-C Newsletter. Thank you for joining the Action-to-Beat Coronavirus (Ab-C) study, unfolding in parallel with the coronavirus pandemic in Canada. Because of your active participation, we have been able to understand the different facets of the COVID pandemic.

Together, we have successfully completed three phases of the Ab-C study. To give a quick overview, we have been tracking the pandemic through your experiences and the presence of COVID antibodies in your dried blood samples. In Phase 1, representing the first viral wave, 2% of study participants were positive for COVID antibodies, depicting a low level of spread in Canada. In Phase 2, after the second viral wave but before most adults were vaccinated, the seroprevalence rose to 5-6%–which includes both the people who had antibodies in Phase 1 plus those who had developed them since then.

We can now report to you the Phase 3 results, based on dried blood samples (DBS) collected from July-September 2021, a time when most Canadian adults were vaccinated. The resulting seroprevalence in Figure 1 is mostly a result of those who developed antibodies in response to the vaccine, but also includes a small proportion who developed them after natural infection, and of course, those who were both vaccinated and infected.

Figure 1. COVID antibody levels (“seroprevalence”) in Canada over time

The rate of full vaccination, meaning at least two doses, is positively correlated with age, with the lowest rates among those under 40 years of age and the highest among those 70 and older. By August 2021, the proportion of the national population with complete vaccination was 61%, while it was 67% among Ab-C participants, confirming that the Ab-C study population is similar to the broader Canadian population. As shown in Figure 2, the seroprevalence with one dose only was highest in the youngest adults, but similar for fully vaccinated people in all adult age groups.

Figure 2. Seroprevalence by age and if adults received one or two vaccine doses

All the COVID vaccines used in Canada resulted in close to 100% of those vaccinated producing antibodies, as shown in Figure 3. The differences between the vaccines were quite small, and even 95% of those with a single dose of the AstraZeneca vaccine produced seroprevalence.

Figure 3. Seroprevalence in adults with one dose or with two doses (or more) in the Ab-C Study

The pandemic is changing, but it is not over. Continuing Ab-C in Phase 4 in early January 2022 is even more important now than it was earlier, as we anticipate a new wave of cases due to existing and new variants of COVID (including Omicron). We will specifically be looking for possible breakthrough infections of the Delta variant. Importantly, we will be able to assess how long the antibodies triggered by vaccination persist, and compare antibody levels right through to Phase 5, which is scheduled for Spring 2022 (Figure 4).

We are incredibly grateful for your participation through the first three phases, and encourage you to stay with us through Phases 4 and 5. Ab-C study participants will get an invitation to continue providing DBSs when the Ab-C study team send you your individual Phase 3 results. Even participants who have not previously given a DBS will be able to provide a sample. Regardless of whether they provide a sample or not, participants will be able to update their COVID experience in a new Angus Reid Forum survey in early December.

Figure 4. Phases of the Ab-C study in relation to when COVID cases and vaccination occurred in Canada

Here is how you can help, whether or not you have been vaccinated: