Seroprevalence of anti-SARS-CoV-2 antibodies 6 months into the vaccination campaign in Geneva, Switzerland, 1 June to 7 July 2021

Abstract

Background Up-to-date seroprevalence estimates are critical to describe the SARS-CoV-2 immune landscape and to guide public health decisions. Aim We estimate seroprevalence of anti-SARS-CoV-2 antibodies 15 months into the COVID-19 pandemic and 6 months into the vaccination campaign. Methods We conducted a population-based cross-sectional serosurvey between 1 June and 7 July 2021, recruiting participants from age- and sex-stratified random samples of the general population. We tested participants for anti-SARS-CoV-2 antibodies targeting the spike (S) or nucleocapsid (N) proteins using the Roche Elecsys immunoassays. We estimated the anti-SARS-CoV-2 antibodies seroprevalence following vaccination and/or infection (anti-S antibodies), or infection only (anti-N antibodies). Results Among 3,355 individuals (54.1% women; 20.8% aged < 18 years and 13.4% aged ≥ 65 years), 2,161 (64.4%) had anti-S antibodies and 906 (27.0%) had anti-N antibodies. The total seroprevalence was 66.1% (95% credible interval (CrI): 64.1–68.0). We estimated that 29.9% (95% Crl: 28.0–31.9) of the population developed antibodies after infection; the rest having developed antibodies via vaccination. Seroprevalence estimates differed markedly across age groups, being lowest among children aged 0–5 years (20.8%; 95% Crl: 15.5–26.7) and highest among older adults aged ≥ 75 years (93.1%; 95% Crl: 89.6–96.0). Seroprevalence of antibodies developed via infection and/or vaccination was higher among participants with higher educational level. Conclusion Most of the population has developed anti-SARS-CoV-2 antibodies, despite most teenagers and children remaining vulnerable to infection. As the SARS-CoV-2 Delta variant spreads and vaccination rates stagnate, efforts are needed to address vaccine hesitancy, particularly among younger individuals and to minimise spread among children.

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

“…SalivaHIS results were compared with other national and international seroprevalence studies that were conducted during the same study period. From these studies it appears that the seroprevalence was 66.1% in the general population in Geneva (July 2021) [ 8 ], 89.4% in the general population in England (July 2021) [ 11 ], 75.9% among blood donors in Austria (July 2021) [ 10 ], and 98.0% (July 2021) among Belgian blood donors [ 12 ]. The seroprevalence of 78.1% (July 2021) observed in our study is, thus, relatively consistent with what was found in those other studies [ 8 , 10 , 11 , 12 ].…”

“…From these studies it appears that the seroprevalence was 66.1% in the general population in Geneva (July 2021) [ 8 ], 89.4% in the general population in England (July 2021) [ 11 ], 75.9% among blood donors in Austria (July 2021) [ 10 ], and 98.0% (July 2021) among Belgian blood donors [ 12 ]. The seroprevalence of 78.1% (July 2021) observed in our study is, thus, relatively consistent with what was found in those other studies [ 8 , 10 , 11 , 12 ]. Of course, these results should be interpreted with caution as the epidemiological situation and the vaccination campaign were different in each country.…”

“…COVID-19 seroprevalence studies have been conducted in several countries; as, among others, in Switzerland [ 8 ], Portugal [ 9 ], Austria [ 10 ], and England [ 11 ]. In Belgium, studies have first been set up in specific population groups such as blood donors [ 12 ], hospital healthcare workers [ 13 ], primary healthcare workers [ 14 ], schoolchildren and school staff [ 15 ], and residents and staff in nursing homes [ 16 ].…”

COVID-19-related school disruptions and well-being of children and adolescents in Geneva

“…In June/July 2021, we conducted a survey selecting a representative sample of children and adolescents of a Swiss canton population (Ethics Committee ID: 2020-0088) [6]. Parents of school-aged children reported information about them missing school because of COVID-19, from August 2020 to June 2021.…”

Severe Acute Respiratory Syndrome Coronavirus 2 Infections in Children

“…These studies show that SARS-CoV-2 infections in children have been frequently underdiagnosed. 12 , 13 , 14 Many of these studies conducted in different countries before 15 , 16 , 17 , 18 and after vaccine availability 19 showed a lower number of infection-derived SARS-CoV-2 antibody detection in children compared to adults. However, country and regional study differences conducted at varying timepoints during the pandemic have reported mixed results.…”