In its latest report, Canadian Blood Services revealed the toll of Omicron’s spread through mid-February 2022. Not only did 22.7% of all blood donors experience a prior SARS-CoV-2 infection, but this rate represented a 35% jump during the 22-day sampling period (January 24 – February 15). Young donors (36.6%) and those self-identifying as a visible minority (32.4%) continue to be most at risk from Omicron’s effects. Mid-February’s seropositivity rate was quadruple that seen in Canadian Blood Services’ seroprevalence reports for the months of March to November 2021.
- Infection-acquired seropositivity (as evidenced by anti-nucleocapsid IgG antibodies) increased 35% throughout the 22-day study period, from 16.3% during the week of January 24-31 to 22.7% by February 15. Consistent with the rapid spread of the Omicron variant, this rate climbed exponentially throughout the study period. As antibodies targeting the nucleocapsid protein1 (anti-N) appear on average one-to-two weeks following symptom onset, this report likely captures infections during the peak of the fifth wave.
- Donors between the ages of 17-24 experienced the highest infection-acquired seropositivity of all age groups at 36.6%.
- Donors belonging to a racialized group continued to experience greater rates of infection-acquired antibodies compared to white donors (32.4% vs. 20.1%).
- In early February, differences in infection-acquired seropositivity continued to be less apparent between socioeconomic quintiles.
- Nearly all (99.7%) blood donors tested positive for antibodies targeting the spike protein, reflecting the high coverage of vaccination and boosters as well as the growing rates of infection.
The latest report builds on January’s report and includes new data from 13,189 people who donated blood from February 1 to 15, 2022, in all Canadian provinces excluding Quebec.
Peak of the fifth wave
Mid-February’s seropositivity rate was quadruple that seen in Canadian Blood Services’ seroprevalence reports for the months of March to November 2021. These findings unmistakably reflect Omicron’s hold. While mid-February’s rate is the highest recorded so far, it may be an underestimation of the toll of past infections due to the seroreversionSeroreversion is defined as a decrease in antibody levels to the point where they are below the threshold of detection of an assay. This occurs naturally with time elapsed since exposure. of anti-N antibodies acquired earlier in the pandemic.
Elevated spike antibody concentrations seen across all ages
The median concentration of spike antibodies, which started to rise in December after dipping in September, were very high across all age groups by mid-February. Recent booster vaccinations are almost certainly behind this increase in concentrations, but new infections may also contribute.
It should be noted that individuals who choose to donate blood are generally in good health and are more likely to live in populous urban areas. Percentages were adjusted for test characteristics and population distribution.
1 Antibodies to the nucleocapsid protein are indicative of a past infection with the virus as COVID-19 vaccines approved and administered in Canada target the spike protein.
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