The gap between the rates of COVID-19 infection and vaccination among racialized and non-racialized Canadians continues to exist, as does the gap between Canadians from lower- and higher-income neighbourhoods. The CITF-funded Canadian Blood Services Serosurveillance Study has released its latest report for the month of May 2021. While the latest data show that the proportion of blood donors with antibodies acquired through vaccination increased substantially in May 2021 (60%) compared to April 2021 (24%), this increase is less pronounced among donors from racialized and lower-income communities. Indeed, these same socioeconomic determinants were also associated with higher rates of antibodies due to infection with SARS-CoV-2.

Key Points:
• In May 2021, seroprevalence due to infection:

  • rose to 4%, up from 3% in April 2021.
  • was 2X as high in racialized donors than in self-declared white donors.
  • was more than 1.5 times higher in donors from neighbourhoods with lower socioeconomic status (based on postal codes) compared to donors living in more affluent neighbourhoods.
  • was highest in blood donors aged 17-24, particularly in Alberta and Manitoba.

• In May 2021, seroprevalence acquired through vaccination:

  • climbed to 60%, up from 24% in April 2021.
  • Increased by 37 percentage points in white blood donors, whereas non-white blood donors saw a 31-percentage point increase, when compared to April 2021. However, the relative increase among the two was similar.
  • increased similarly among donors from lower- and higher-income neighbourhoods, with a 7-percentage point gap between the two, when compared to April 2021.

The latest CBS data included 17,001 people who donated blood between May 22 and June 4, 2021, in all Canadian provinces (excluding Quebec). Results show that seroprevalence due to infection, i.e., the number of people with antibodies to SARS-CoV-2 due to a past infection, was 4.0%, up from 3.2% in April 2021.

Persistent socioeconomic inequalities among infection rates

The rate of seroprevalence due to past infection with SARS-CoV-2 in racialized donors (7.4%) was more than double that of donors who self-identified as white (3.3.%). Moreover, donors living in lower-income neighbourhoods, as measured by the Material Deprivation Index based on postal codes, were 1.7X more likely to have evidence of a past infection with SARS-CoV-2 (5.7%) than donors living in higher-income neighbourhoods (3.1%).

As indicative from previous surveys, seroprevalence due to SARS-CoV-2 infection in May 2021 was highest in those aged 17 to 24 years (7.0%), compared to other age groups. This was particularly apparent in Alberta and Manitoba, where the seroprevalence due to infection in 17- to 24-year-olds was 12.7% and 11.3%, respectively.

Overall, Canada’s levels of seroprevalence due to a past SARS-CoV-2 infection remained low in May 2021, while the roll-out of vaccines was in full swing.

Vaccine-induced immunity skyrockets, though vaccine inequality still present

Indeed, the proportion of blood donors with antibodies to SARS-CoV-2 acquired through vaccination rose to 59.8% in May 2021, a 2.5X increase from April 2021 at 23.6%. Similar to infection rates, inequality in vaccine-induced seroprevalence was observed among socioeconomic groups. Blood donors who self-identified as white were 1.3X more likely to have vaccine-induced immunity (61.8%) than donors belonging to racialized groups (48.9%), such as Indigenous, Asian, and other People of Colour. Likewise, donors living in higher-income neighbourhoods were more likely to have antibodies acquired through vaccination (64.8%) than donors living in lower-income neighbourhoods (56.6%). While the gap between the rates of vaccine-induced seroprevalence among racialized and non-racialized Canadians and among Canadians from lower and higher socio-economic neighbourhoods was still present, it was relatively narrower in May 2021 than it was April 2021.

CITF analysis

These results suggest that the consequences of the variant-fueled third wave were concentrated in poorer neighbourhoods and amongst racialized communities. Current efforts to protect these communities with vaccines need renewed focus, particularly with the fourth wave looming. There is clearly a need to incentivize the 17-24-year-old age group to get vaccinated, especially with the imminent arrival of in-class learning for high school and university students: this age group had the highest level of previous COVID-19 infection (detected by antibodies) yet the lowest rate of vaccination.