Critical Care Workers Have Lower Seroprevalence of SARS-CoV-2 IgG Compared with Non-patient Facing Staff in First Wave of COVID19.

INTRODUCTION: In early 2020, at first surge of the coronavirus disease 2019 (COVID-19) pandemic, many health care workers (HCW) were re-deployed to critical care environments to support intensive care teams looking after patients with severe COVID-19. There was considerable anxiety of increased risk of COVID-19 for these staff. To determine whether critical care HCW were at increased risk of hospital acquired infection, we explored the relationship between workplace, patient facing role and evidence of immune exposure to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) within a quaternary hospital providing a regional critical care response. Routine viral surveillance was not available at this time. METHODS: We screened over 500 HCW (25% of the total workforce) for history of clinical symptoms of possible COVID19, assigning a symptom severity score, and quantified SARS-CoV-2 serum antibodies as evidence of immune exposure to the virus. RESULTS: Whilst 45% of the cohort reported symptoms that they consider may have represented COVID-19, 14% had evidence of immune exposure. Staffs in patient facing critical care roles were least likely to be seropositive (9%) and staff working in non-patient facing roles most likely to be seropositive (22%). Anosmia and fever were the most discriminating symptoms for seropositive status. Older males presented with more severe symptoms. Of the 12 staff screened positive by nasal swab (10 symptomatic), 3 showed no evidence of seroconversion in convalescence. CONCLUSIONS: Patient facing staff working in critical care do not appear to be at increased risk of hospital acquired infection however the risk of nosocomial infection from non-patient facing staff may be more significant than previous recognised. Most symptoms ascribed to possible COVID-19 were found to have no evidence of immune exposure however seroprevalence may underrepresent infection frequency. Older male staff were at the greatest risk of more severe symptoms.

A functional assay for serum detection of antibodies against SARS-CoV-2 nucleoprotein.

The humoral immune response to SARS-CoV-2 results in antibodies against spike (S) and nucleoprotein (N). However, whilst there are widely available neutralization assays for S antibodies, there is no assay for N-antibody activity. Here, we present a simple in vitro method called EDNA (electroporated-antibody-dependent neutralization assay) that provides a quantitative measure of N-antibody activity in unpurified serum from SARS-CoV-2 convalescents. We show that N antibodies neutralize SARS-CoV-2 intracellularly and cell-autonomously but require the cytosolic Fc receptor TRIM21. Using EDNA, we show that low N-antibody titres can be neutralizing, whilst some convalescents possess serum with high titres but weak activity. N-antibody and N-specific T-cell activity correlates within individuals, suggesting N antibodies may protect against SARS-CoV-2 by promoting antigen presentation. This work highlights the potential benefits of N-based vaccines and provides an in vitro assay to allow the antibodies they induce to be tested.

A thermostable, closed SARS-CoV-2 spike protein trimer.

The spike (S) protein of SARS-CoV-2 mediates receptor binding and cell entry and is the dominant target of the immune system. It exhibits substantial conformational flexibility. It transitions from closed to open conformations to expose its receptor-binding site and, subsequently, from prefusion to postfusion conformations to mediate fusion of viral and cellular membranes. S-protein derivatives are components of vaccine candidates and diagnostic assays, as well as tools for research into the biology and immunology of SARS-CoV-2. Here we have designed mutations in S that allow the production of thermostable, disulfide-bonded S-protein trimers that are trapped in the closed, prefusion state. Structures of the disulfide-stabilized and non-disulfide-stabilized proteins reveal distinct closed and locked conformations of the S trimer. We demonstrate that the designed, thermostable, closed S trimer can be used in serological assays. This protein has potential applications as a reagent for serology, virology and as an immunogen.