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

Prevalence of SARS-CoV-2 antibodies and associated factors in the adult population of Belgium: a general population cohort study between March 2021 and April 2022

BACKGROUND

This study assessed seroprevalence trends of SARS-CoV-2 antibodies in the Belgian adult population between March 2021 and April 2022, and explored factors associated with seropositivity and seroreversion among the vaccinated and unvaccinated population.

METHODS

A prospective longitudinal surveillance study was conducted within a random sample of the general population (18 + years) in Belgium, selected from the national register through a multistage sampling design. Participants provided a saliva sample and completed a survey questionnaire on three occasions: at baseline and in two follow-up waves. Outcome variables included (1) seropositivity, defined as the presence of SARS-CoV-2 antibodies, assessed with a semi-quantitative measure of anti-RBD (Receptor Binding Domain) IgG ELISA and (2) seroreversion, defined as passing from a positive to a negative antibody test between two measurements. Trends in SARS-CoV-2 antibody prevalence were assessed using binary logistic regression with contrasts applying post-stratification. Potential determinants of seropositivity were assessed through multilevel logistic regressions.

RESULTS

In total 6,178 valid observations were obtained from 2,768 individuals. SARS-CoV-2 antibody prevalence increased from 25.1% in the beginning of the study period to 92.3% at the end. Among the vaccinated population, factors significantly associated with higher seropositivity rates were being younger, having a bachelor diploma, living with others, having had a vaccine in the last 3 months and having received a nucleic-acid vaccine or a combination. Lower seropositivity rates were observed among vaccinated people with a neurological disease and transplant patients. Factors significantly associated with higher seropositivity rates among the unvaccinated population were having non-O blood type and being non-smoker. Among vaccinated people, the seroreversion rate was much lower (0.3%) in those who had received their latest vaccine in the last 3 months compared to those who had received their latest vaccine more than 3 months ago (2.7%) (OR 0.13; 95%CI 0.04-0.42).

CONCLUSIONS

The rapid increase in antibody seropositivity in the general adult population in Belgium during the study period was driven by the vaccination campaign which ran at full speed during this period. Among vaccinated people, seropositivity varied in function of the time since last vaccine, the type of vaccine, sociodemographic features and health status.

Geography Influences Susceptibility to SARS-CoV-2 Serological Response in Patients With Inflammatory Bowel Disease: Multinational Analysis From the ICARUS-IBD Consortium

BACKGROUND

Beyond systematic reviews and meta-analyses, there have been no direct studies of serological response to COVID-19 in patients with inflammatory bowel disease (IBD) across continents. In particular, there has been limited data from Asia, with no data reported from India. The ICARUS-IBD (International study of COVID-19 Antibody Response Under Sustained immunosuppression in IBD) consortium assessed serological response to SARS-CoV-2 in patients with IBD in North America, Europe, and Asia.

METHODS

The ICARUS-IBD study is a multicenter observational cohort study spanning sites in 7 countries. We report seroprevalence data from 2303 patients with IBD before COVID-19 vaccination between May 2020 and November 2021. SARS-CoV-2 anti-spike and anti-nucleocapsid antibodies were analyzed.

RESULTS

The highest and lowest SARS-CoV-2 anti-spike seropositivity rates were found in Asia (81.2% in Chandigarh and 57.9% in Delhi, India; and 0% in Hong Kong). By multivariable analysis, country (India: odds ratio [OR], 18.01; 95% confidence interval [CI], 12.03-26.95; P < .0001; United Kingdom: OR, 2.43; 95% CI, 1.58-3.72; P < .0001; United States: OR, 2.21; 95% CI, 1.27-3.85; P = .005), male sex (OR, 1.46; 95% CI, 1.07-1.99; P = .016), and diabetes (OR, 2.37; 95% CI, 1.04-5.46; P = .039) conferred higher seropositivity rates. Biological therapies associated with lower seroprevalence (OR, 0.22; 95% CI, 0.15-0.33; P < .0001). Multiple linear regression showed associations between anti-spike and anti-nucleocapsid titers with medications (P < .0001) but not with country (P = .3841).

CONCLUSIONS

While the effects of medications on anti-SARS-CoV-2 antibody titers in patients with IBD were consistent across sites, geographical location conferred the highest risk of susceptibility to serologically detectable SARS-CoV-2 infection. Over half of IBD patients in India were seropositive prior to vaccination. These insights can help to inform shielding advice, therapeutic choices, and vaccine strategies in IBD patients for COVID-19 and future viral challenges.

Reversed urban-rural gradient in COVID-19 seroprevalence and related factors in a nationally representative survey, Poland, 29 March to 14 May 2021

BackgroundWe anticipated that people in rural areas and small towns with lower population density, lower connectivity and jobs less dependent on social interaction will be less exposed to COVID-19. Still, other variables correlated with socioeconomic inequalities may have a greater impact on transmission.AimWe investigated how COVID-19 affected rural and urban communities in Poland, focussing on the most exposed groups and disparities in SARS-CoV-2 transmission.MethodsA random digit dial sample of Polish adults stratified by region and age was drawn from 29 March to 14 May 2021. Serum samples were tested for anti-S1 and anti-N IgG antibodies, and positive results in both assays were considered indicative of past infection. Seroprevalence estimates were weighted to account for non-response. Adjusted odds ratios (AORs) were calculated using multivariable logistic regression.ResultsThere was serological evidence of infection in 32.2% (95% CI: 30.2-34.4) of adults in rural areas/small towns (< 50,000 population) and 26.6% (95% CI: 24.9-28.3) in larger cities. Regional SARS-CoV-2 seroprevalence ranged from 23.4% (95% CI: 18.3-29.5) to 41.0% (95% CI: 33.5-49.0) and was moderately positively correlated (R = 0.588; p = 0.017; n = 16) with the proportion of respondents living in rural areas or small cities. Upon multivariable adjustment, both men (AOR = 1.60; 95% CI: 1.09-2.35) and women (AOR = 2.26; 95% CI: 1.58-3.21) from these areas were more likely to be seropositive than residents of larger cities.ConclusionsWe found an inverse urban-rural gradient of SARS-CoV-2 infections during early stages of the COVID-19 pandemic in Poland and suggest that vulnerabilities of populations living in rural areas need to be addressed.

Seroprevalence of SARS-CoV-2 Antibodies in Denmark: Results of Two Nationwide Population-Based Surveys, February and May 2021

Background

Seroprevalence studies can be used to measure the progression of national COVID-19 epidemics. The Danish National Seroprevalence Survey of SARS-CoV-2 infections (DSS) was conducted as five separate surveys between May 2020 and May 2021. Here, we present results from the two last surveys conducted in February and May 2021.

Methods

Persons aged 12 or older were randomly selected from the Danish Population Register and those having received COVID-19 vaccination subsequently excluded. Invitations to have blood drawn in local test centers were sent by mail. Samples were analyzed for whole Immunoglobulin by ELISA. Seroprevalence was estimated by sex, age and geography. Comparisons to vaccination uptake and RT-PCR test results were made.

Results

In February 2021, we found detectable antibodies in 7.2% (95% CI: 6.3-7.9%) of the invited participants (participation rate 25%) and in May 2021 in 8.6% (95% CI: 7.6-9.5%) of the invited (participation rate: 14%). Seroprevalence did not differ by sex, but by age group, generally being higher among the <50 than 50+ year-olds. In May 2021, levels of seroprevalence varied from an estimated 13% (95% CI: 12-15%) in the capital to 5.2% (95% CI: 3.4-7.4%) in rural areas. Combining seroprevalence results with vaccine coverage, estimates of protection against infection in May 2021 varied from 95% among 65+ year-olds down to 10-20% among 12-40 year-olds. In March-May 2021, an estimated 80% of all community SARS-CoV-2 infections were diagnosed by RT-PCR and captured by surveillance.

Conclusion

Seroprevalence estimates doubled during the 2020-21 winter wave of SARS-CoV-2 infections and then stabilized as vaccinations were rolled out. The epidemic affected large cities and younger people the most. Denmark saw comparatively low infections rates, but high test coverage; an estimated four out of five infections were detected by RT-PCR in March-May 2021.

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

OBJECTIVES

To estimate the prevalence, incidence and longevity of antibodies against SARS-CoV-2 among primary healthcare providers (PHCPs).

DESIGN

Prospective cohort study with 12 months of follow-up.

SETTING

Primary care in Belgium.

PARTICIPANTS

Any general practitioner (GP) working in primary care in Belgium and any other PHCP from the same GP practice who physically manages (examines, tests, treats) patients were eligible. A convenience sample of 3648 eligible PHCPs from 2001 GP practices registered for this study (3044 and 604 to start in December 2020 and January 2021, respectively). 3390 PHCPs (92,9%) participated in their first testing time point (2820 and 565, respectively) and 2557 PHCPs (70,1%) in the last testing time point (December 2021).

INTERVENTIONS

Participants were asked to perform a rapid serological test targeting IgM and IgG against the receptor binding domain of SARS-CoV-2 and to complete an online questionnaire at each of maximum eight testing time points.

PRIMARY AND SECONDARY OUTCOME MEASURES

The prevalence, incidence and longevity of antibodies against SARS-CoV-2 both after natural infection and after vaccination.

RESULTS

Among all participants, 67% were women and 77% GPs. Median age was 43 years. The seroprevalence in December 2020 (before vaccination availability) was 15.1% (95% CI 13.5% to 16.6%), increased to 84.2% (95% CI 82.9% to 85.5%) in March 2021 (after vaccination availability) and reached 93.9% (95% CI 92.9% to 94.9%) in December 2021 (during booster vaccination availability and fourth (delta variant dominant) COVID-19 wave). Among not (yet) vaccinated participants the first monthly incidence of antibodies against SARS-CoV-2 was estimated to be 2.91% (95% CI 1.80% to 4.01%). The longevity of antibodies is higher in PHCPs with self-reported COVID-19 infection.

CONCLUSIONS

This study confirms that occupational health measures provided sufficient protection when managing patients. High uptake of vaccination resulted in high seroprevalence of SARS-CoV-2 antibodies in PHCPs in Belgium. Longevity of antibodies was supported by booster vaccination and virus circulation.

TRIAL REGISTRATION NUMBER

NCT04779424.

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

OBJECTIVES

Gathering population-based data on prevalence of SARS-CoV-2 infection is vital to the public health response and planning. Current seroprevalence data in BC are limited with respect to considerations of how socioeconomic and demographic factors, such as age, sex, gender, income, identifying as a visibility minority and occupation, are related to SARS-CoV-2 antibody detection due to infection-acquired immunity. We aimed to estimate the SARS-CoV-2 seropositivity in a cohort of British Columbians, using at-home self-collected dried blood spot (DBS) samples.

DESIGN

This cross-sectional study included online surveys that collected sociodemographic and COVID-19 vaccine receipt information, and an at-home DBS collection kit.

SETTING

British Columbia (BC), Canada.

PARTICIPANTS

Eligible participants were aged 25-69 years and residents of BC.

PRIMARY OUTCOME MEASURE

SARS-CoV-2 anti-spike IgG antibody detection in unvaccinated individuals. Adjusted incidence rate ratios (aIRR) explored factors associated with seropositivity.

RESULTS

SARS-CoV-2 serology was performed on a total of 4048 unvaccinated participants 25-69 years of age who submitted DBS samples taken from November 2020 to June 2021. A total of 118 seropositive cases were identified, for an estimated overall seropositivity of 2.92% (95% CI 2.42% to 3.48%). Participants identifying as a visible minority had a higher seropositivity, 5.1% vs 2.6% (p=0.003), compared with non-visible minority participants. After adjustment by age and sex, identifying as a visible minority (aIRR=1.85, 95% CI 1.20 to 2.84) remained the only significant factor associated with SARS-CoV-2 antibody detection in this cohort of unvaccinated individuals.

CONCLUSIONS

SARS-CoV-2 seropositivity in the BC population due to infection-acquired immunity was low. Seropositivity indicated that among those unvaccinated, visible minority communities have been most impacted. Continued monitoring of SARS-CoV-2 serology due to both infection-acquired and vaccine-acquired immunity will be vital in public health planning and pandemic response.