Prevalence of Anti-SARS-CoV-2 Antibodies and Potential Determinants among the Belgian Adult Population: Baseline Results of a Prospective Cohort Study

Abstract

The prevalence of anti-SARS-CoV-2 antibodies and potential determinants were assessed in a random sample representative of the Belgian adult population. In total, 14,201 individuals (≥18 years) were invited by mail to provide saliva via an Oracol® swab. Survey weights were applied, and potential determinants were estimated using multivariable logistic regressions. Between March and August 2021, 2767 individuals participated in the first data collection. During this period, which coincided with the onset of the vaccination campaign, the seroprevalence in the population increased from 25.2% in March/April to 78.1% in July. Among the vaccinated there was an increase from 74,2% to 98.8%; among the unvaccinated, the seroprevalence remained stable (around 17%). Among the vaccinated, factors significantly associated with the presence of antibodies were: having at least one chronic disease (ORa 0.22 (95% CI 0.08–0.62)), having received an mRNA-type vaccine (ORa 5.38 (95% CI 1.72–16.80)), and having received an influenza vaccine in 2020–2021 (ORa 3.79 (95% CI 1.30–11.07)). Among the unvaccinated, having a non-O blood type (ORa 2.00 (95% CI 1.09–3.67)) and having one or more positive COVID-19 tests (ORa 11.04 (95% CI 4.69–26.02)) were significantly associated. This study provides a better understanding of vaccine- and/or natural-induced presence of anti-SARS-CoV-2 antibodies and factors that are associated with this presence.

Prevalence, incidence and longevity of antibodies against SARS-CoV-2 among primary healthcare providers in Belgium: a prospective cohort study with 12 months of follow-up

“…Compared with the study protocol, the testing time point at the fifth month was skipped because of limited additional epidemiological value based on progressive insights from studies with similar protocols conducted by Sciensano that longer interval than 4 weeks between testing time point are suitable. [13][14][15][16][17] Sample size This study aimed to include 5000 PHCPs with a ratio of 4 GPs to 1 other PHCP. The sample size considerations regarding the different objectives of the proposed study are described in more detail in the study protocol.…”

Seropositivity of SARS-CoV-2 in an unvaccinated cohort in British Columbia, Canada: a cross-sectional survey with dried blood spot samples

“…[22][23][24] In countries with a similar socioeconomic profile as Canada, the estimated seroprevalence has varied widely, with 0.1% seroprevalence in New Zealand at the end of 2020, 5.6% in England in October-November 2020, 20.2% in the USA from July Open access Open access 2020 to May 2021, and 17% between March and August 2021 in unvaccinated Belgian adults. [25][26][27][28] The factors significantly associated with seropositivity in this cohort included identifying as a visible minority and working as an essential heath care worker. Both of these factors have been identified in other jurisdictions as being highly associated with COVID-19.…”

The prevalence, incidence and longevity of antibodies against SARS-CoV-2 among primary healthcare providers in Belgium: a prospective cohort study with 12 months of follow-up

“…Compared to the study protocol, the testing timepoint at the fifth month was skipped because of limited additional epidemiological value based on progressive insights from studies with similar protocols conducted by Sciensano that longer interval than four weeks between testing time point are suitable. 13-17…”

“…Compared to the study protocol, the testing timepoint at the fifth month was skipped because of limited additional epidemiological value based on progressive insights from studies with similar protocols conducted by Sciensano that longer interval than four weeks between testing time point are suitable. [13][14][15][16][17] Sample size This study aimed to include 5,000 PHCPs with a ratio of 4 GPs to 1 other PHCP. The sample size considerations regarding the different objectives of the proposed study are described in more detail in the study protocol.…”

“…9,10 Additionally, after vaccination, longevity of antibody positivity could differ depending on the type of vaccination and vaccination regime. 11,12 For Belgium, Sciensano (the Belgian national institute of public health, www.sciensano.be) performs national seroprevalence studies of SARS-CoV-2 antibodies in the general population 13 and several relevant populations including school-aged children and school staff, 14 hospital staff, 15 nursing homes residents and their staff. 16,17 These results are publicly available and regularly updated on an online dashboard.…”