Research indicates that Canadians typically obtain hybrid immunity to SARS-CoV-2 through natural infection, mainly from the Omicron variant, and vaccination, but seropositivity varies depending on age and location.
An analysis of over 900,000 blood samples collected between March 2020 and March 2023 revealed that 76% of the Canadian population had antibodies produced by infection as detectable by March 22-24.
Dr Bruce Mazer
According to Bruce D. Mazer, MD, associate scientific director of the COVID-19 Immunity Task Force (CITF), and David L. Buckeridge, PhD, scientific lead, both of McGill University in Montreal, Quebec, reported that the findings were crucial for understanding the pandemic and preparing for future pandemics, as stated by Medscape Medical News.
Dr David Buckeridge
The study analyzed mortality rates and the risk of illness in young individuals, as well as the ability of older people to protect themselves from infection.
The study also revealed that individuals from racialized groups and those living in less privileged areas had higher rates of infection-acquired immunity during the pandemic, prompting the need for targeted public health initiatives.
The Canadian Medical Association Journal published the study on August 14.
The youth population is spreading.
The investigators used a time-series approach to estimate trends in SARS-CoV-2 seroprevalence from infection to vaccination, using the three intervals of prevaccination (March to November 2020), vaccine rollout (December 2020 to October 2021), and the arrival of the Omicron variant between January and March 2023.
The data was obtained from a total of seven research studies, which involved collecting over 900,000 samples.
The CITF and the investigation was conducted in tandem.
Humoural immunity to SARS-CoV-2 was present in 9% of Canadians by November 2021 from infection. However, the Omicron variant caused a significant increase in seroprevalence, which increased to 47% by mid-June 2022 and then to 6.4% on average every month between December 15 and July 2023.
During the summer, there was a gradual increase in rates. In 2022, infection-acquired seroprevalence rapidly increased and then stabilized in March 2023, when approximately 76% of the population had antibodies from infections.
The rate of seropositivity increased more rapidly during the Omicron waves among younger age groups. In mid-June 2022, people under 25 years were 57% more likely to have acquired infection-acquired seroprevalence, followed by those aged 25 to 39 years (51%), 40 to 59 years (40%), and 60 years and older (25%).
Provincial serosurveys showed similar patterns, with the highest rates of seroprevalence being in children and adolescents. The Western provinces of Manitoba, Saskatchewan, Alberta, and British Columbia had the most prevalence of infection-induced antibodies.
The study reveals that infection-induced humoral immunity was similarly stimulated in many countries by the Omicron wave, but due to differences in population seropositivity across age and geography, the potential for lower antibody levels, and new variants that may escape immunity, public health policy and clinical decisions should be tailored to local patterns of population immunity.
Keep your eyes peeled on the future.
Mazer and Buckeridge have created the CITF Databank, which is expected to provide Canada with better preparation for emerging pathogens.
Currently, clinicians recommend keeping an eye on vulnerable individuals during the pandemic, particularly those who were elderly and had medical conditions that put them at risk of complications.
“In order to assess the risk of infection and immunity for their patients, clinicians must also comprehend its broader implications.”
“Canada’s vaccination-induced immunity was likely responsible for our lower mortality rates during the Omicron wave, as we learned from O micron that the virus is constantly changing, just like influenza, which means we need to ensure those at risk are vaccinated according to current guidelines.”
Is there a similarity between the US and other countries?
Anna Bershteyn, PhD, an assistant professor of population health at NYU Grossman School of Medicine in New York City and a former advisor to the NewYorK City Department of Health and Mental Hygiene on COVID-19 forecasting, provided her opinion on the findings for Medscape.
Dr Anna Bershteyn is a member of the Royal College of Nursing and one year old.
The US experienced a significant rise in the proportion of people with SARS-CoV-2 infection-induced antibodies during the Omicron wave, similar to Canada’s experience. However, the percentage of individuals with infection caused this increase before O micron was introduced, possibly due to larger and denser cities than those in other parts of the US. Bershteyn did not participate in any research.
She stressed that the study should not be misinterpreted as a failure of vaccines to protect the public from the Omicron wave. “Vaccines were designed to minimize severe disease consequences such as hospitalization and death, and it is evident that they helped save lives and gave rise to hybrid immunity that most Canadians and Americans have today.”
The COVID-19 Immunity Task Force provided funding for these projects, which were also supported by the Public Health Agency of Canada (PHAC). Buckeridge has received funding from PHACC in support of the current research. Mazer and Bershteyn have no relevant financial connections.
The complete article of CMAJ was made available online on August 14, 2023.
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