Serial cross-sectional estimation of vaccine-and infection-induced SARS-CoV-2 seroprevalence in British Columbia, Canada

Abstract

The British Columbia Centre for Disease Control (BCCDC) has a longestablished serosurvey protocol to monitor population susceptibility to emerging or re-emerging respiratory viruses. The approach was first deployed during the influenza A (H1N1) pandemic in 2009 to monitor changes in seroprevalence across successive pandemic waves and the mass vaccination campaign. [1][2][3][4][5][6][7] The methodology is predicated upon serial cross-sectional convenience sampling of anonymized residual sera from children and adults of all ages in the most populated Lower Mainland region of BC. 8,9 Adapting this protocol, the BCCDC launched its first SARS-CoV-2 serosurvey in March 2020, just before the World Health Organization's declaration of the COVID-19 pandemic. 10 Baseline assessment was followed by additional serosurveys that spanned the time from mRNA vaccine availability in mid-December 2020, through 7 pandemic waves associated with multiple variants of concern to August 2022 (Figure 1). [11][12][13] Using these serosurveys, we sought to track the evolving proportion of the population that remained

Real-world COVID-19 vaccine effectiveness against the Omicron BA.2 variant in a SARS-CoV-2 infection-naive population

“…Our Omicron IAR estimates over time were lower than those reported in South Africa (58% in urban areas by April 2022) 20 , Denmark (66% by March 2022) 21 , Navarre, Spain (up to 59% by May 2022) 22 and British Columbia, Canada (up to 61% by July–August 2022) 23 likely reflecting the effectiveness of extensive public health and social measures imposed in Hong Kong during the fifth wave, such as a universal mask mandate with high community compliance, closure of all bars, and limits on opening hours and new ventilation requirements in all restaurants 24 , counteracted by the very high density of Hong Kong’s residential dwellings facilitating rapid aerosol transmission between apartments 25 .…”

Comparison of influenza and COVID-19 hospitalisations in British Columbia, Canada: a population-based study

“…27 Specifically, seroprevalence study in BC showed that at least 63% of children under the age of 5 were infected by March 2022, at time when few were vaccinated. 28 To the best of our knowledge, we could only compare our annual analysis findings with published literature due to unavailability of population-level studies since Omicron emerged. Our findings are similar to other studies reporting higher rates of hospitalisation for COVID-19 compared with influenza in unvaccinated populations in the early phases of the pandemic.…”

Prior infection- and/or vaccine-induced protection against Omicron BA.1, BA.2 and BA.4/BA.5-related hospitalisations in older adults: a test-negative case-control study in Quebec, Canada

“…Among our BA.4/5 controls, we identified 15% with a prior infection compared to 40% in the same age group in sero-prevalence studies conducted in July-August 2022 in Quebec and British Columbia, Canada. 13,28 Missed prior infections in the reference group of unvaccinated "uninfected" individuals would result in underestimation of the protection induced by prior infection and hybrid immunity. VE among "uninfected" individuals would be underestimated if the proportion of missed prior infections among vaccinated individuals was smaller than the unvaccinated "uninfected" group, but would be overestimated if their proportion of missed prior infections was higher.…”

“…Owing to their greater risk of severe outcomes, elderly adults ≥60 years of age have been prioritized for COVID-19 vaccination since the start of the pandemic. Sero-prevalence data in Canada, the United States, United Kingdom and elsewhere show age-related decrease in cumulative SARS-CoV-2 infection rates across the pandemic [12][13][14][15] Infections foremost accrued during successive omicron waves, with at least 70% of Canadian children and young adults and about half of elderly adults having been infected by autumn 2022. 12,13 The accumulating percentage of the elderly population with prior history of both SARS-CoV-2 infection and repeat vaccination has likely modified their baseline risk.…”

“…Sero-prevalence data in Canada, the United States, United Kingdom and elsewhere show age-related decrease in cumulative SARS-CoV-2 infection rates across the pandemic [12][13][14][15] Infections foremost accrued during successive omicron waves, with at least 70% of Canadian children and young adults and about half of elderly adults having been infected by autumn 2022. 12,13 The accumulating percentage of the elderly population with prior history of both SARS-CoV-2 infection and repeat vaccination has likely modified their baseline risk. However, most VE analyses and booster dose policies have not taken into account this relevant and evolving immuno-epidemiological context.…”