Influence of age, sex, body habitus, vaccine type and anti-S serostatus on cellular and humoral responses to SARS-CoV-2 vaccination (preprint)

Vaccine development targeting SARS-CoV-2 in 2020 was of critical importance in reducing COVID-19 severity and mortality. In the U.K. during the initial roll-out most individuals either received two doses of Pfizer COVID-19 vaccine (BNT162b2) or the adenovirus-based vaccine from Oxford/AstraZeneca (ChAdOx1-nCoV-19). There are conflicting data as to the impact of age, sex and body habitus on cellular and humoral responses to vaccination, and most studies in this area have focused on determinants of mRNA vaccine immunogenicity. Here we studied a cohort of participants in a population-based longitudinal study (COVIDENCE UK) to determine the influence of age, sex, body mass index (BMI) and pre-vaccination anti-Spike (anti-S) antibody status on vaccine-induced humoral and cellular immune responses to two doses of BNT162b2 or ChAdOx-n-CoV-19 vaccination. Younger age and pre-vaccination anti-S seropositivity were both associated with stronger antibody responses to vaccination. BNT162b2 generated higher neutralising and anti-S antibody titres to vaccination than ChAdOx1-nCoV-19, but cellular responses to the two vaccines were no different. Irrespective of vaccine type, increasing age was also associated with decreased frequency of cytokine double-positive CD4+ T cells. Increasing BMI was associated with reduced frequency of SARS-CoV-2-specific TNF+ CD8% T cells for both vaccines. Together, our findings demonstrate that increasing age and BMI associate with attenuated cellular and humoral responses to SARS-CoV-2 vaccination. Whilst both vaccines induced T cell responses, BNT162b2 induced significantly elevated humoral immune response as compared to ChAdOx-n-CoV-19.

SARS-CoV-2 infection is associated with anti-desmoglein 2 autoantibody detection. (preprint)

Post-acute cardiac sequelae, following SARS-CoV-2 infection, are well recognised as complications of COVID-19. We have previously shown the persistence of autoantibodies against antigens in skin, muscle, and heart in individuals following severe COVID-19; the most common staining on skin tissue displayed an inter-cellular cement pattern consistent with antibodies against desmosomal proteins. Desmosomes play a critical role in maintaining the structural integrity of tissues. For this reason, we analysed desmosomal protein levels and the presence of anti-desmoglein (DSG) 1, 2 and 3 antibodies in acute and convalescent sera from patients with COVID 19 of differing clinical severity. We find increased levels of DSG2 protein in sera from acute COVID patients. Furthermore, we find that DSG2 autoantibody levels are increased significantly in convalescent sera following severe COVID-19 but not in hospitalised patients recovering from influenza infection or healthy controls. Levels of autoantibody in sera from patients with severe COVID-19 were comparable to levels in patients with non-COVID-19-associated cardiac disease, potentially identifying DSG2 autoantibodies as a novel biomarker for cardiac damage. To determine if there was any association between severe COVID-19 and DSG2, we stained post-mortem cardiac tissue from patients who died from COVID-19 infection. This revealed disruption of the intercalated disc between cardiomyocytes that was consistent with separation of the DSG2 protein homodimer. Our results reveal the potential for DSG2 protein and autoimmunity to DSG2 to contribute to unexpected pathologies associated with COVID-19 infection.

Increased seroprevalence and improved antibody responses following third primary SARS-CoV-2 immunisation: an update from the COV-AD study (preprint)

BackgroundPatients with primary and secondary antibody deficiency are vulnerable to COVID-19 and demonstrate diminished responses following two-dose SARS-CoV-2 vaccine schedules. Third primary vaccinations have been deployed to enhance their humoral and cellular immunity. ObjectivesTo determine the immunogenicity of the third primary SARS-CoV-2 immunisation in a heterogeneous cohort of patients with antibody deficiency. MethodsParticipants enrolled in the COV-AD study were sampled before and after their third vaccine dose. Serological and cellular responses were determined using ELISA, live-virus neutralisation and ELISPOT assays. ResultsA third primary SARS-CoV-2 vaccine significantly increased anti-spike glycoprotein antibody seroprevalence from 61.4% to 76.0%, the magnitude of the antibody response, its neutralising capacity and induced seroconversion in individuals who were seronegative after two vaccine doses. Vaccine-induced serological responses were broadly cross-reactive against the SARS-CoV-2 B.1.1.529 variant of concern, however, overall seroprevalence and antibody levels remained significantly lower than healthy controls. No differences in serological responses were observed between individuals who received the AstraZeneca ChAdOx1 nCoV-19 and Pfizer BioNTech 162b2 during their initial two-dose vaccine schedule. SARS-CoV-2 infection naive participants who had received a heterologous vaccine as a third dose were significantly more likely to have a detectable T cell responses following their third vaccine dose (61.5% vs 11.1%). ConclusionThese data support the widespread use of third primary immunisations to enhance humoral immunity against SARS-CoV-2 in individuals with antibody deficiency.

Correlation between post-vaccination titres of combined IgG, IgA, and IgM anti-Spike antibodies and protection against breakthrough SARS-CoV-2 infection: a population-based longitudinal study (COVIDENCE UK) (preprint)

In this population-based cohort of 7530 adults, combined IgG/A/M anti-Spike titres measured after SARS-CoV-2 vaccination were predictive of protection against breakthrough SARS-CoV-2 infection. Discrimination was significantly improved by adjustment for factors influencing risk of SARS-CoV-2 exposure including household overcrowding, public transport use, and visits to indoor public places.

Cross reactivity of spike glycoprotein induced antibody against delta and omicron variants before and after third SARS-CoV-2 vaccine dose (preprint)

Variants of SARS-CoV-2 may evade natural and vaccine induced immunity and monoclonal antibody immunotherapeutics. There is an urgent need to know how well antibodies, induced by healthy and Clinically Extremely Vulnerable (CEV) patients, will bind and thus help reduce transmission and severity of infection from variants of concern (VOC). This study determines the cross-reactive binding of serum antibodies obtained prior to and 28 days after a third vaccination in three cohorts; a health care worker cohort who received three doses of Pfizer-BioNtech (PPP), a cohort of CEV patients received two doses of the AstraZeneca-ChAdOx1-nCoV-19 (AAP) vaccine, followed by a third PFZ vaccine and a haemodialysis cohort that had a mixture of two AZ or PFZ vaccines followed by a PFZ booster. Six months post second vaccine there was evidence of antibody waning with 58.9% of individuals in the HD cohort seropositive against Wuhan, 34.4% Delta and 62.2% Omicron strains. For the AAP cohort, equivalent figures were 62.5%, 45.8% and 91.7% and the PPP cohort 92.2%, 90% and 91.1%. Post third dose vaccination there were universal increases in seropositivity and median optical density. For the HD cohort, 98.8% were seropositive to the Wuhan strain, 97.6% against Delta and 100% against Omicron strains. For the PPP and AAP cohorts, 100% were seropositive against all 3 strains. Lastly, we examined the WHO NIBSC 20/136 standard and there was no loss of antibody binding to either VOC. Similarly, a dilution series of Sotrovimab (GSK) found this therapeutic monoclonal antibody bound similarly to all VOC.

In vitro, classical complement activation differs by disease severity and between SARS-CoV-2 antigens (preprint)

Antibodies specific for the spike glycoprotein (S) and nucleocapsid (N) SARS-CoV-2 proteins are typically present during severe COVID-19, and induced to S after vaccination. The binding of viral antigens by antibody can initiate the classical complement pathway. Since complement could play pathological or protective roles at distinct times during SARS-CoV-2 infection we determined levels of antibody-dependent complement activation along the complement cascade. Here, we used an ELISA assay to assess complement protein binding (C1q) and the deposition of C4b, C3b, and C5b to S and N antigens in the presence of anti-SARS-CoV-2 antibodies from different test groups: non-infected, single and double vaccinees, non-hospitalised convalescent (NHC) COVID-19 patients and convalescent hospitalised (ITU-CONV) COVID-19 patients. C1q binding correlates strongly with antibody responses, especially IgG1 levels. However, detection of downstream complement components, C4b, C3b and C5b shows some variability associated with the antigen and subjects studied. In the ITU-CONV, detection of C3b-C5b to S was observed consistently, but this was not the case in the NHC group. This is in contrast to responses to N, where median levels of complement deposition did not differ between the NHC and ITU-CONV groups. Moreover, for S but not N, downstream complement components were only detected in sera with higher IgG1 levels. Therefore, the classical pathway is activated by antibodies to multiple SARS-CoV-2 antigens, but the downstream effects of this activation may differ depending on the specific antigen targeted and the disease status of the subject. O_LISpike- and nucleocapsid-specific antibodies activate complement in vitro C_LIO_LIC1q binding correlates with IgG1 antibody levels C_LIO_LIGeneration of C4b, C3b and C5b relates to the antigen targeted and the patient group tested C_LI

Determinants of pre-vaccination antibody responses to SARS-CoV-2: a population-based longitudinal study (COVIDENCE UK) (preprint)

Background: Prospective population-based studies investigating multiple determinants of pre-vaccination antibody responses to SARS-CoV-2 are lacking. Methods: We did a prospective population-based study in SARS-CoV-2 vaccine-naive UK adults between May 1 and Nov 2, 2020. Information on 88 potential risk factors was obtained through online questionnaires, and combined IgG/IgA/IgM responses to SARS-CoV-2 spike glycoprotein were determined in dried blood spots. We used logistic and linear regression to estimate adjusted odds ratios (aORs) and adjusted geometric mean ratios (aGMRs) for potential determinants of SARS-CoV-2 seropositivity (all participants) and antibody titres (seropositive participants only), respectively. Results: 1696 (15.2%) of 11,130 participants were seropositive. Factors independently associated with increased risk included frontline health/care occupation (aOR 1.86, 95% CI 1.49-2.33), international travel (1.22, 1.08-1.37), BMI >30 vs <25 kg/m2 (1.22, 1.05-1.42), Asian/Asian British vs White ethnicity (1.65, 1.10-2.47), and alcohol consumption [≥]15 vs 0 units/week (1.26, 1.06-1.49). Light physical exercise associated with decreased risk (0.80, 0.69-0.93, for [≥]10 vs 0-4 h/week). Higher titres associated with frontline health/care occupation (aGMR 1.26, 95% CI 1.13-1.41), international travel (1.10, 1.04-1.16), BMI >30 vs <25 kg/m2 (1.09, 1.01-1.17), and Asian/Asian British vs White ethnicity (1.23, 1.03-1.46); these associations were not substantially attenuated by adjustment for disease severity. Conclusions: Higher alcohol consumption and reduced physical exercise represent new modifiable risk factors for SARS-CoV-2 infection. Recognised associations between Asian/Asian British ethnic origin and obesity and increased risk of SARS-CoV-2 seropositivity were independent of other sociodemographic, clinical, or behavioural factors investigated.

Longitudinal protection following natural SARS-CoV-2 infection and early vaccine responses: insights from a cohort of community based dental health care professionals (preprint)

Abstract Background The threshold of protection for anti-SARS-CoV-2 spike glycoprotein antibodies and their longevity are not known. Interpretation of serological results in with respect to international reference material can inform this essential question. Methods 1,507 West Midlands dental care professionals were recruited into this study in June 2020. Baseline seroprevalence of antibodies directed against the SARS-CoV-2 spike glycoprotein was determined and the cohort was followed longitudinally for 6 months until January/February 2021 through the second wave of the COVID-19 pandemic in the United Kingdom, and commencement of vaccination. Results Baseline seroprevalence was 16.3% in this cohort, compared to estimates in the general population of between 6-7%. Seropositivity was retained in over 70% of participants at 3 and 6-month follow up and conferred a 74% reduced risk of infection. During follow-up, no PCR-proven infections occurred in individuals with a baseline anti-SARS-CoV-2 IgG level greater than 147.6 IU/ml with respect to the World Health Organization international standard 20-136. Post-vaccination, antibody responses were more rapid and of higher magnitude in individuals with who were seropositive at baseline. Conclusion Natural infection leads to a serological response that remains detectable in over 70% of individuals 6 months after initial sampling and 9 months from the peak of the first wave of the pandemic. This response is associated with protection from future infection. Even if serological responses wane, a single dose of the Pfizer-BioNTech vaccine is associated with an antibody response indicative of immunological memory. Funding The Association of Clinical Biochemistry and Laboratory Medicine and The Institute for Global Innovation (IGI) of the University of Birmingham.

Diagnostic accuracy of Loop mediated isothermal amplification coupled to Nanopore sequencing for the detection of SARS-CoV-2 infection at scale in symptomatic and asymptomatic populations (preprint)

IntroductionRapid, high throughput diagnostics are a valuable tool, allowing the detection of SARS-CoV-2 in populations, in order to identify and isolate people with asymptomatic and symptomatic infections. Reagent shortages and restricted access to high throughput testing solutions have limited the effectiveness of conventional assays such as reverse transcriptase quantitative PCR (RT-qPCR), particularly throughout the first months of the COVID-19 pandemic. We investigated the use of LamPORE, where loop mediated isothermal amplification (LAMP) is coupled to nanopore sequencing technology, for the detection of SARS-CoV-2 in symptomatic and asymptomatic populations. MethodsIn an asymptomatic prospective cohort, for three weeks in September 2020 health care workers across four sites (Birmingham, Southampton, Basingstoke and Manchester) self-swabbed with nasopharyngeal swabs weekly and supplied a saliva specimen daily. These samples were tested for SARS-CoV-2 RNA using the Oxford Nanopore LamPORE system and a reference RT-qPCR assay on extracted sample RNA. A second retrospective cohort of 848 patients with influenza like illness from March 2020 - June 2020, were similarly tested from nasopharyngeal swabs. ResultsIn the asymptomatic cohort a total of 1200 participants supplied 23,427 samples (3,966 swab, 19,461 saliva) over a three-week period. The incidence of SARS-CoV-2 detection using LamPORE was 0.95%. Diagnostic sensitivity and specificity of LamPORE was >99.5% in both swab and saliva asymptomatic samples when compared to the reference RT-qPCR test. In the retrospective symptomatic cohort, the incidence was 13.4% and the sensitivity and specificity were 100%. ConclusionsLamPORE is a highly accurate methodology for the detection of SARS-CoV-2 in both symptomatic and asymptomatic population settings and can be used as an alternative to RT-qPCR.

Validation of a combined ELISA to detect IgG, IgA and IgM antibody responses to SARS-CoV-2 in mild or moderate non-hospitalised patients (preprint)

BackgroundFrequently SARS-CoV-2 results in mild or moderate disease with potentially lower concentrations of antibodies compared to those that are hospitalised. Here, we validated an ELISA using SARS-CoV-2 trimeric spike glycoprotein, with targeted detection of IgG, IgA and IgM (IgGAM) using serum and dried blood spots (DBS) from adults with mild or moderate disease. MethodsTargeting the SARS-CoV-2 trimeric spike, a combined anti-IgG, IgA and IgM serology ELISA assay was developed using 62 PCR-confirmed non-hospitalised, mild or moderate COVID-19 samples, [≥]14 days post symptom onset and 624 COVID-19 negative samples. The assay was validated using 73 PCR-confirmed non-hospitalised COVID-19 and 359 COVID-19 negative serum samples with an additional 81 DBSs, and further validated in 226 PCR-confirmed non-hospitalised COVID-19 and 426 COVID-19 negative clinical samples. ResultsA sensitivity and specificity of 98.6% (95% CI, 92.6-100.0), 98.3% (95% CI, 96.4-99.4), respectively, was observed following validation of the SARS-CoV-2 ELISA. No cross-reactivities with endemic coronaviruses or other human viruses were observed, and no change in results were recorded for interfering substances. The assay was stable at temperature extremes and components were stable for 15 days once opened. A matrix comparison showed DBS to correlate with serum results. Clinical validation of the assay reported a sensitivity of 94.7% (95% CI, 90.9-97.2%) and a specificity of 98.4% (95% CI, 96.6-99.3%). ConclusionsThe human anti-IgGAM SARS-CoV-2 ELISA provides accurate and sensitive detection of SARS-CoV-2 antibodies in non-hospitalised adults with mild or moderate disease. The use of dried blood spots makes the assay accessible to the wider community. Supplementary MaterialNo

Serological responses to SARS-CoV-2 following non-hospitalised infection: clinical and ethnodemographic features associated with the magnitude of the antibody response (preprint)

Objective To determine clinical and ethnodemographic correlates of serological responses against the SARS-CoV-2 spike glycoprotein following mild-to-moderate COVID-19. Design A retrospective cohort study of healthcare workers who had self-isolated due to COVID-19. Setting University Hospitals Birmingham NHS Foundation Trust, UK (UHBFT). Participants 956 health care workers were recruited by open invitation via UHBFT trust email and social media. Intervention Participants volunteered a venous blood sample that was tested for the presence of anti-SARS-CoV-2 spike glycoprotein antibodies. Results were interpreted in the context of the symptoms of their original illness and ethnodemographic variables. Results Using an assay that simultaneously measures the combined IgG, IgA and IgM response against the spike glycoprotein (IgGAM), the overall seroprevalence within this cohort was 46.2% (n=442/956). The seroprevalence of immunoglobulin isotypes was 36.3%, 18.7% and 8.1% for IgG, IgA and IgM respectively. IgGAM identified serological responses in 40.6% (n=52/128) of symptomatic individuals who reported a negative SARS-CoV-2 PCR test. Increasing age, non-white ethnicity and obesity were independently associated with greater IgG antibody response against the spike glycoprotein. Self-reported fever and fatigue were associated with greater IgG and IgA responses against the spike glycoprotein. The combination of fever and/or cough and/or anosmia had a positive predictive value of 92.3% for seropositivity. Conclusions and relevance Assays employing combined antibody detection demonstrate enhanced seroepidemiological sensitivity and can detect prior viral exposure even when PCR swabs have been negative. We demonstrate an association between known ethnodemographic risk factors associated with mortality from COVID-19 and the magnitude of serological responses in mild-to-moderate disease. The combination of cough, and/or fever and/or anosmia identifies the majority of individuals who should self-isolate for COVID-19.

Vitamin D status and seroconversion for COVID-19 in UK healthcare workers who isolated for COVID-19 like symptoms during the 2020 pandemic. (preprint)

Background: It is clear that in UK healthcare workers, COVID-19 infections and deaths were more likely to be in staff who were of BAME origin. This has led to much speculation about the role of vitamin D in healthcare worker COVID-19 infections. We aimed to determine the prevalence of vitamin D deficiency in NHS staff who have isolated with symptoms suggestive of COVID-19 and relate this to vitamin D status. Methods: We recruited NHS healthcare workers between 12th to 22nd May 2020 as part of the COVID-19 convalescent immunity study (COCO). We measured anti-SARS-Cov-2 antibodies using a combined IgG, IgA and IgM ELISA (The Binding Site). Vitamin D status was determined by measurement of serum 25(OH)D3 using the AB SCIEX Triple Quad 4500 mass spectrometry system. Findings: Of the 392 NHS healthcare workers, 214 (55%) had seroconverted for COVID-19. A total of 61 (15{middle dot}6%) members of staff were vitamin D deficient (<30 nmol/l) with significantly more staff from BAME backgrounds or in a junior doctor role being deficient. Vitamin D levels were lower in those who were younger, had a higher BMI (>30 kg/m2), and were male. Multivariate analysis revealed that BAME and COVID-19 seroconversion were independent predictors of vitamin D deficiency. Staff who were vitamin D deficient were more likely to self-report symptoms of body aches and pains but importantly not the respiratory symptoms of cough and breathlessness. Vitamin D levels were lower in those COVID-19 positive staff who reported fever, but this did not reach statistical significance. Within the whole cohort there was an increase in seroconversion in staff with vitamin D deficiency compared to those without vitamin D deficiency (n=44/61, 72% vs n=170/331, 51%; p=0{middle dot} 003); this was particularly marked in the proportion of BAME males who were vitamin D deficient compared to non-vitamin D deficient BAME males (n=17/18, 94% vs n=12/23, 52%; p=0{middle dot}005). Multivariate analysis revealed that vitamin D deficiency was an independent risk factor for seroconversion (OR 2{middle dot}6, 95%CI 1{middle dot}41- 4{middle dot} 80; p=0{middle dot}002). Interpretation: In those healthcare workers who have isolated due to symptoms of COVID-19, those of BAME ethnicity are at the highest risk of vitamin D deficiency. Vitamin D deficiency is a risk factor for COVID-19 seroconversion for NHS healthcare workers especially in BAME male staff.

Sensitive detection of SARS-CoV-2-specific-antibodies in dried blood spot samples (preprint)

ImportancePopulation-wide serological testing is an essential component in understanding the COVID-19 pandemic. The logistical challenges of undertaking widespread serological testing could be eased through use of a reliable dried blood spot (DBS) sampling method. ObjectiveTo validate the use of dried blood spot sampling for the detection of SARS-CoV-2-specific antibodies. Design, setting and participantsEighty-seven matched DBS and serum samples were obtained from eighty individuals, including thirty-one who were previously PCR-positive for SARS-CoV-2. DBS eluates and sera were used in an ELISA to detect antibodies to the viral spike protein. ResultsSpecific anti-SARS-Cov-2 spike glycoprotein antibodies were detectable in both serum and DBS eluate and there was a significant correlation between the antibody levels detected in matched samples (r = 0.96, p<0.0001). Using serum as the gold standard in the assay, matched DBS samples achieved a Cohens kappa coefficient of 0.975 (near-perfect agreement), a sensitivity of 98.1% and specificity of 100%, for detecting anti-spike glycoprotein antibodies. Conclusions and relevanceEluates from DBS samples are a reliable and reproducible source of antibodies to be used for the detection of SARS-CoV-2-specific antibodies. The use of DBS sampling could complement the use of venepuncture in the immunosurveillance of COVID-19 in both low and high income settings.

Detection of antibodies to the SARS-CoV-2 spike glycoprotein in both serum and saliva enhances detection of infection (preprint)

Background: Detecting antibody responses during and after SARS-CoV-2 infection is essential in determining the seroepidemiology of the virus and the potential role of antibody in disease. Scalable, sensitive and specific serological assays are essential to this process. The detection of antibody in hospitalized patients with severe disease has proven straightforward; detecting responses in subjects with mild disease and asymptomatic infections has proven less reliable. We hypothesized that the suboptimal sensitivity of antibody assays and the compartmentalization of the antibody response may contribute to this effect. Methods: We systemically developed an ELISA assay, optimising different antigens and amplification steps, in serum and saliva from symptomatic and asymptomatic SARS-CoV-2-infected subjects. Results: Using trimeric spike glycoprotein, rather than nucleocapsid enabled detection of responses in individuals with low antibody responses. IgG1 and IgG3 predominate to both antigens, but more anti-spike IgG1 than IgG3 was detectable. All antigens were effective for detecting responses in hospitalized patients. Anti-spike, but not nucleocapsid, IgG, IgA and IgM antibody responses were readily detectable in saliva from non-hospitalized symptomatic and asymptomatic individuals. Antibody responses in saliva and serum were largely independent of each other and symptom reporting. Conclusions. Detecting antibody responses in both saliva and serum is optimal for determining virus exposure and understanding immune responses after SARS-CoV-2 infection. Funding. This work was funded by the University of Birmingham, the National Institute for Health Research (UK), the NIH National Institute for Allergy and Infectious Diseases, the Bill and Melinda Gates Foundation and the University of Southampton.

Serology confirms SARS-CoV-2 infection in PCR-negative children presenting with Paediatric Inflammatory Multi-System Syndrome (preprint)

Background. During the COVID-19 outbreak, reports have surfaced of children who present with features of a multisystem inflammatory syndrome with overlapping features of Kawasaki disease and toxic shock syndrome - Paediatric Inflammatory Multisystem Syndrome- temporally associated with SARS-CoV-2 pandemic (PIMS-TS). Initial reports find that many of the children are PCR-negative for SARS-CoV-2, so it is difficult to confirm whether this syndrome is a late complication of viral infection in an age group largely spared the worst consequences of this infection, or if this syndrome reflects enhanced surveillance. Methods. Children hospitalised for symptoms consistent with PIMS-TS between 28 April and 8 May 2020, and who were PCR-negative for SARS-CoV-2, were tested for antibodies to viral spike glycoprotein using an ELISA test. Results. Eight patients (age range 7-14 years, 63% male) fulfilled case-definition for PIMS-TS during the study period. Six of the eight patients required admission to intensive care. All patients exhibited significant IgG and IgA responses to viral spike glycoprotein. Further assessment showed that the IgG isotypes detected in children with PIMS-TS were of the IgG1 and IgG3 subclasses, a distribution similar to that observed in samples from hospitalised adult COVID-19 patients. In contrast, IgG2 and IgG4 were not detected in children or adults. IgM was not detected in children, which contrasts with adult hospitalised adult COVID-19 patients of whom all had positive IgM responses. Conclusions. Strong IgG antibody responses can be detected in PCR-negative children with PIMS-TS. The low detection rate of IgM in these patients is consistent with infection having occurred weeks previously and that the syndrome onset occurs well after the control of SARS-CoV-2 viral load. This implies that the disease is largely immune-mediated. Lastly, this indicates that serology can be an appropriate diagnostic tool in select patient groups.

SARS-CoV-2 seroconversion in health care workers (preprint)

Background The correlates of protection against SARS-CoV-2 and their longevity remain unclear. Studies in severely ill individuals have identified robust cellular and humoral immune responses against the virus. Asymptomatic infection with SARS-CoV-2 has also been described, but it is unknown whether this is sufficient to produce antibody responses. Methods We performed a cross-sectional study recruiting 554 health care workers from University Hospitals Birmingham NHS Foundation Trust who were at work and asymptomatic. Participants were tested for current infection with SARS-CoV-2 by nasopharyngeal swab for real-time polymerase chain reaction and for seroconversion by the measurement of anti-SARS-CoV-2 spike glycoprotein antibodies by enzyme linked immunosorbent assay. Results were interpreted in the context of previous, self-reported symptoms of illness consistent with COVID-19. Results The point prevalence of infection with SARS-CoV-2, determined by the detection of SARS-CoV-2 RNA on nasopharnygeal swab was 2.39% (n=13/544). Serum was available on 516 participants. The overall rate of seroconversion in the cohort was 24.4% (n=126/516). Individuals who had previously experienced a symptomatic illness consistent with COVID-19 had significantly greater seroconversion rates than those who had remained asymptomatic (37.5% vs 17.1%, {chi}2 =21.1034, p<0.0001). In the week preceding peak COVID-19-related mortality at UHBFT, seroconversion rates amongst those who were suffering from symptomatic illnesses peaked at 77.8%. Prior symptomatic illness generated quantitatively higher antibody responses than asymptomatic seroconversion. Seroconversion rates were highest amongst those working in housekeeping (34.5%), acute medicine (33.3%) and general internal medicine (30.3%) with lower rates observed in participants working in intensive care (14.8%) and emergency medicine (13.3%). Conclusions In a large cross-sectional seroprevalence study of health-care workers, we demonstrate that asymptomatic seroconversion occurs, however prior symptomatic illness is associated with quantitatively higher antibody responses. The identification that the potential for seroconversion in health-care workers can associate differentially with certain hospital departments may inform future infection control and occupational health practices.