In the first of a series of biweekly reports, the Canadian Blood Services revealed Omicron’s traction in December 2021. While all blood donors tested positive for the spike (S) protein, primarily due to immunization, infection-acquired seropositivity (as evidenced by anti-N IgG antibodies) climbed from 7.5% to 10.1 % from December 25, 2021 to January 15, 2022. This latter rate is roughly double the monthly average in 2021, further highlighting the impact of Omicron. Inequities persist among racialized donors, who are consistently twice as likely to have infection-acquired antibodies compared to white donors. Younger donors (aged 17 to 24) have the highest infection-acquired seropositivity rate, at 20.2%, continuing the trend seen throughout 2021.

Key findings:

  • Nearly all blood donors tested positive for antibodies targeting the spike protein, most commonly due to vaccination.
  • Infection-acquired seropositivity (as evidenced by anti-N IgG antibodies) climbed 35% throughout the 22-day study period, from 7.5% to 10.1 %.
  • In early January, infection-acquired seropositivity increased in all Canadian provinces compared to early December (excludes Quebec).

The latest report includes 17,927 people who donated blood from January 1 to 15, 2022, in all Canadian provinces excluding Quebec.

Omicron’s impact evidenced in donor blood

Antibodies targeting the nucleocapsid protein of SARS-CoV-21 appear on average one-to-two weeks following symptom onset. Hence, this report likely captures antibody-evidence from infections up to the 2021 holiday period. January’s seropositivity rate of up to 10.1% is nearly double that seen in the Canadian Blood Services’ monthly seroprevalence reports in 2021. These findings clearly reflect Omicron gaining hold. This, at a time when diagnostic PCR tests became unavailable for large swaths of the Canadian population.

It should also be noted that donors with a known active SARS-CoV-2 infection are not eligible to donate blood until their infection and symptoms have cleared (at least 14 days).

Inequity in infection burden persists

As previously reported, evidence of a prior infection was twice as likely in self-identified racialized donors (16.8%) compared to white donors (8.6%). On the other hand, in early January, differences in infection-acquired seropositivity were less apparent between the various socioeconomic quintiles.

Spike antibodies on the rise across all ages

The median concentration of spike antibodies, which started to dip in September, increased substantially by early January 2022. Increased concentrations were noticeable across all age groups, but particularly among those aged 60+. This is consistent with the rollout of third (booster) vaccine doses as a rise in the concentration of spike antibodies is expected after vaccination. Increases in spike antibody concentrations may also be indicative of a recent infection. This suggests that both the number of boosters administered and the Omicron-driven fifth wave may be at play.

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.

Explore our interactive webpage updated every month, featuring the latest aggregated data gathered by the Canadian Blood Services and Héma-Québec on SARS-CoV-2 seroprevalence in Canada.

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, thus permitting the distinction.