Journal Article

Hybrid immunity from severe acute respiratory syndrome coronavirus 2 infection and vaccination in Canadian adults: A cohort study

Tang, Xuyang, Gingras, Anne-Claude, Reid, Angus, Bansal, Aiyush, Brown, Patrick E, Bogoch, Isaac I, Birnboim, H Chaim, Slutsky, Arthur S, Fu, Sze Hang, Colwill, Karen, Lam, Teresa, Delgado-Brand, Melanie, Qi, Freda, Pasic, Maria D, Mailhot, Geneviève, Tursun, Tulunay, Morawski, Ed, Nagelkerke, Nico, Companion, Jeffrey, Newcombe, Leslie, Jha, Prabhat

2024

Overview

Few national-level studies have evaluated the impact of 'hybrid' immunity (vaccination coupled with recovery from infection) from the Omicron variants of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). From May 2020 to December 2022, we conducted serial assessments (each of ~4000-9000 adults) examining SARS-CoV-2 antibodies within a mostly representative Canadian cohort drawn from a national online polling platform. Adults, most of whom were vaccinated, reported viral test-confirmed infections and mailed self-collected dried blood spots (DBSs) to a central lab. Samples underwent highly sensitive and specific antibody assays to spike and nucleocapsid protein antigens, the latter triggered only by infection. We estimated cumulative SARS-CoV-2 incidence prior to the Omicron period and during the BA.1/1.1 and BA.2/5 waves. We assessed changes in antibody levels and in age-specific active immunity levels. Spike levels were higher in infected than in uninfected adults, regardless of vaccination doses. Among adults vaccinated at least thrice and infected more than 6 months earlier, spike levels fell notably and continuously for the 9-month post-vaccination. In contrast, among adults infected within 6 months, spike levels declined gradually. Declines were similar by sex, age group, and ethnicity. Recent vaccination attenuated declines in spike levels from older infections. In a convenience sample, spike antibody and cellular responses were correlated. Near the end of 2022, about 35% of adults above age 60 had their last vaccine dose more than 6 months ago, and about 25% remained uninfected. The cumulative incidence of SARS-CoV-2 infection rose from 13% (95% confidence interval 11-14%) before omicron to 78% (76-80%) by December 2022, equating to 25 million infected adults cumulatively. However, the coronavirus disease 2019 (COVID-19) weekly death rate during the BA.2/5 waves was less than half of that during the BA.1/1.1 wave, implying a protective role for hybrid immunity. Strategies to maintain population-level hybrid immunity require up-to-date vaccination coverage, including among those recovering from infection. Population-based, self-collected DBSs are a practicable biological surveillance platform. Funding was provided by the COVID-19 Immunity Task Force, Canadian Institutes of Health Research, Pfizer Global Medical Grants, and St. Michael's Hospital Foundation. PJ and ACG are funded by the Canada Research Chairs Program.

• Publisher: eLife Sciences Publications Ltd
• Subject: Adult / Aged / Antibodies / Antibodies, Viral - blood / Antibodies, Viral - immunology / Antigens / Canada - epidemiology / Cohort Studies / Coronaviruses / COVID-19 / COVID-19 - epidemiology / COVID-19 - immunology / COVID-19 - prevention & control / COVID-19 diagnostic tests / COVID-19 vaccines / COVID-19 Vaccines - administration & dosage / COVID-19 Vaccines - immunology / Diabetes / Drug dosages / Epidemiology / Female / Humans / Immunity / immunology / Infections / infectious diseases / Male / Middle Aged / Mortality / Nucleocapsids / Population / Proteins / Public health / SARS-CoV-2 - immunology / Severe acute respiratory syndrome coronavirus 2 / Spike Glycoprotein, Coronavirus - immunology / Vaccination / Young Adult