This is a summary, written by members of the CITF Secretariat, of Héma-Québec’s Phase 4b (June) report to the CITF and the Ministère de la Santé et des Services sociaux du Québec. The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

The latest serosurvey conducted by Héma-Québec estimates that 45.3% of adults in Quebec developed infection-acquired antibodies to SARS-CoV-2 between December 2021 and June 2022, up from 27.3% in mid-March 2022. Antibodies against the nucleocapsid (N) protein of SARS-CoV-2, which is indicative of a previous infection, was highest among younger individuals (18-25 years, at 72.1%) and lowest among older individuals (>65 years, at 30.2%). This suggests that young people remain the primary vector for SARS-CoV-2 transmission in the province.

Key findings:

  • Québec had an increase from 27.3% in mid-March 2022 to 45.3% at the end of June 2022.
  • Between December 2021 and June 2022, the seroprevalence was 72.1% in individuals aged 18-25 and 30.2% in individuals aged >65.
  • Between December 2021 and June 2022, the seroprevalence was 49.1% in individuals aged 26-45 years and 46.0% in individuals aged 46-65 years old.
  • Anti-N seroprevalence was similar in men (46.5%) and women (42.8%) between December 2021 and June 2022.

Conclusion

Due to the lack of sensitivity of the conventional approach, which uses a seropositive threshold that distinguishes between anti-N seropositive from seronegative individuals, a new ratio approach was developed. This new approach provided a more accurate estimate of individuals with a recent infection by obtaining longitudinal samples per individual to determine seropositivity during a given period. The ratio approach estimated 45.3% of anti-N seroprevalence in Quebec between December 2021 and June 2022.

This report includes 558 people (who are all part of the who donated plasma on three occasions between the period in question. The majority of donors were Caucasian and the proportion of men (76%) was greater than women (24%). Donors in the greater Montreal area were underrepresented. Using the ratio approach anti-N seroprevalence was determined based on region, age, and sex for the periods between December 2021 and March 2022, between March 2022 and June 2022, and between December 2021 and June 2022 (aggregate of these two periods).

It should 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). Seropositivity 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.