SARS-CoV-2 antibody seroprevalence in children and workers from Belgian French-speaking primary schools (preprint)

BackgroundDuring the COVID-19 pandemic in 2020, closing schools was discussed as a protective measure to limit the transmission of the virus in Belgium. There was however a lack of evidence on the role of young children in the spread of the virus. We undertook a study among Belgian primary schools in order to assess the seroprevalence of SARS-CoV-2 antibodies and its relationship with communal incidence, size of schools and socio-economic index.MethodThe prospective non-interventional study was conducted from January 14 to May 18, 2021, into 11 primary schools in Belgium during 6 weeks per school. Schools were purposively selected using extremes on 3 criteria: area with a low/high official COVID-19 incidence after the first wave, small/large size of the school, and low/high socio-economic index of the school. Out of 2488 children and 444 school staff invited to participate, 932 (38%) children and 242 (55%) school staff signed an informed consent. Each participant was tested for COVID-19 antibodies using a rapid finger prick test. Additional analysis was conducted to document the low participation rate.ResultsParticipation of children was positively correlated with participation of school staff (r=+0.33;95%CI [-0.34;0.78]), but the correlation was much stronger with socio-economic index (r=+0.81;95%CI [0.40;0.95]). SARS-CoV-2 antibody seroprevalence was lower among children (191/922=21%;95%CI [18-23%]) than among school staff (61/240=25%;95%CI [20-31%]), and it was not correlated with communal cumulative incidence (r=+0.06;95%CI [-0.59;0.67] in children and r=+0.26;95%CI [-0.40;0.74] in school staff). In school staff, seroprevalence was increasing with socio-economic index (r=+0.37;95%CI [-0.29;0.79]), but not in children (r=-0.10;95%CI [-0.66;0.53]). Seroprevalence didn’t present classroom clusters (intraclass correlation coefficient R²=0.08 in children and R2=0.12 in children with school staff).ConclusionIn children, participation was low in schools with a low socio-economic index. Children had a lower seroprevalence than school staff and there were no classroom clusters, suggesting that they are not the transmitters.Trial registrationThe protocol, informed consent forms, and questionnaires were approved by the Hospital-Faculty Ethics Committee Saint-Luc (“Commission d’Ethique hospitalo -facultaire des Cliniques universitaires Saint-Luc”) – UCLouvain, approval number: 2020/16NOV/552. It was registered on clinicaltrials.gov on 16/09/2021, identifier number: NCT05046470, and on ISRCTN on 20/04/2022, identifier number: ISRCTN16837012.

Comprehensive immunovirological and environmental screening reveals risk factors for fatal COVID-19 during post-vaccination nursing home outbreaks (preprint)

COVID-19 vaccination has resulted in excellent protection against fatal disease, including in the elderly. However, risk factors for post-vaccination fatal COVID-19 are largely unknown. We comprehensively studied three large nursing home outbreaks (20-35% fatal cases) by combining SARS-CoV-2 aerosol monitoring, whole-genome phylogenetic analysis, and immunovirological profiling by digital nCounter transcriptomics. Phylogenetic investigations indicated each outbreak stemmed from a single introduction event, though with different variants (Delta, Gamma, and Mu). SARS-CoV-2 was detected in aerosol samples up to 52 days after the initial infection. Combining demographic, immune and viral parameters, the best predictive models for mortality comprised IFNB1 or age, viral ORF7a and ACE2 receptor transcripts. Comparison with published pre-vaccine fatal COVID-19 signatures and reanalysis of single-cell RNAseq data highlights the unique immune signature in post-vaccine fatal COVID-19 outbreaks. A multi-layered strategy including environmental sampling, immunomonitoring, and early antiviral therapy should be considered to prevent post-vaccination COVID-19 mortality in nursing homes.