COVID-19 remains a significant driver of healthcare utilisation. Despite widespread immunity from natural infection and vaccination severe disease and adverse outcomes are still observed, albeit at a reduced frequency. Identifying individuals ‘at risk’ of deterioration at the point of presentation is challenging, however vital to inform decision making around the setting, intensity and escalation of care.

Abstract Introduction Clinical chemistry assays are responsible for 57% of all core lab testing (1) as a result there is an ever-increasing demand to improve the accuracy and reliability of results in clinical laboratories. Sigma metrics have proven to be powerful tools for quantitatively evaluating clinical assay and instrument performance. The Sigma performance of an assay is calculated from the formula (TEa-Bias)/CV. To address modern clinical laboratory performance requirements Abbott has developed and launched a portfolio of clinical chemistry assays under the brand name Sigma STRONG ™ which claim to achieve world class performance with a Sigma Metric of ≥6 for 86% of products within this portfolio (2). The purpose of this study is to assess these assays against Abbott’s products requirement (PR) for precision and method comparison. Methods Assay precision (%CV) studies were performed based on guidance from CLSI EP05-A3 using 2–3 levels of commercially available serum-based control material. Method Comparison (MC) studies were performed based on guidance from CLSI EP09-A3 using the Passing-Bablok regression method. Assays under investigation were assessed for performance on either the Abbott Alinity c or Abbott ARCHITECT c systems. Results Conclusion This study has confirmed the sigma STRONG ™ assays, under assessment, have met Abbott’s product requirement for both precision and method comparison.

BACKGROUND:Natural and vaccine-induced immunity will play a key role in controlling the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. SARS-CoV-2 variants have the potential to evade natural and vaccine-induced immunity. METHODS:In a longitudinal cohort study of healthcare workers (HCWs) in Oxfordshire, United Kingdom, we investigated the protection from symptomatic and asymptomatic polymerase chain reaction (PCR)-confirmed SARS-CoV-2 infection conferred by vaccination (Pfizer-BioNTech BNT162b2, Oxford-AstraZeneca ChAdOx1 nCOV-19) and prior infection (determined using anti-spike antibody status), using Poisson regression adjusted for age, sex, temporal changes in incidence and role. We estimated protection conferred after 1 versus 2 vaccinations and from infections with the B.1.1.7 variant identified using whole genome sequencing. RESULTS:In total, 13 109 HCWs participated; 8285 received the Pfizer-BioNTech vaccine (1407 two doses), and 2738 the Oxford-AstraZeneca vaccine (49 two doses). Compared to unvaccinated seronegative HCWs, natural immunity and 2 vaccination doses provided similar protection against symptomatic infection: no HCW vaccinated twice had symptomatic infection, and incidence was 98% lower in seropositive HCWs (adjusted incidence rate ratio 0.02 [95% confidence interval {CI} < .01-.18]). Two vaccine doses or seropositivity reduced the incidence of any PCR-positive result with or without symptoms by 90% (0.10 [95% CI .02-.38]) and 85% (0.15 [95% CI .08-.26]), respectively. Single-dose vaccination reduced the incidence of symptomatic infection by 67% (0.33 [95% CI .21-.52]) and any PCR-positive result by 64% (0.36 [95% CI .26-.50]). There was no evidence of differences in immunity induced by natural infection and vaccination for infections with S-gene target failure and B.1.1.7. CONCLUSIONS:Natural infection resulting in detectable anti-spike antibodies and 2 vaccine doses both provide robust protection against SARS-CoV-2 infection, including against the B.1.1.7 variant.

Dear editor, Whilst COVID-19 represents a self-limiting disease in most patients infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a small proportion of individuals may develop life threatening respiratory and multi-organ failure associated with prolonged hospital admission and intensive care stay1Guan Wei-jie Ni Zheng-yi Hu Yu Liang Wen-hua Ou Chun-quan He Jian-xing et al.Clinical characteristics of coronavirus disease 2019 in China.N Engl J Med. 2020; 382 (Doi:): 1708-1720https://doi.org/10.1056/nejmoa2002032Google Scholar. In the United Kingdom (UK), same-day emergency care (SDEC) units operating an ambulatory-care-by-default model review a high volume of patients at risk of developing severe disease where rapid decisions must be made regarding treatment and the setting of care delivery, predominantly based on prediction of risk of deterioration1Guan Wei-jie Ni Zheng-yi Hu Yu Liang Wen-hua Ou Chun-quan He Jian-xing et al.Clinical characteristics of coronavirus disease 2019 in China.N Engl J Med. 2020; 382 (Doi:): 1708-1720https://doi.org/10.1056/nejmoa2002032Google Scholar. To support attending clinicians, models incorporating age, comorbidities, clinical metrics and blood test results (particularly C-reactive protein) have been established that estimate the risk of adverse clinical outcomes, encompassing the need for intensive care unit (ICU) admission, non-invasive ventilation (NIV), or death2Gupta Rishi K. Harrison Ewen M. Ho Antonia Docherty Annemarie B. Knight Stephen R. van Smeden Maarten et al.Development and validation of the ISARIC 4C Deterioration model for adults hospitalised with COVID-19: a prospective cohort study.Lancet Respir Med. 2021; (Doi:)https://doi.org/10.1016/S2213-2600(20)30559-2Google Scholar,3Knight Stephen R. Ho Antonia Pius Riinu Buchan Iain Carson Gail Drake Thomas M. et al.Risk stratification of patients admitted to hospital with covid-19 using the ISARIC WHO clinical characterisation protocol: development and validation of the 4C Mortality Score.BMJ. 2020; 370 (Doi:)https://doi.org/10.1136/bmj.m3339Google Scholar. Calprotectin is a cytosolic protein with pro-inflammatory signalling properties released by activated neutrophils. Both an elevated circulating calprotectin concentration and excessive neutrophil degranulation have been mechanistically associated with severe COVID-19 disease4Silvin Aymeric Chapuis Nicolas Dunsmore Garett Goubet Anne Gaëlle Dubuisson Agathe Derosa Lisa et al.Elevated calprotectin and abnormal myeloid cell subsets discriminate severe from mild COVID-19.Cell. 2020; 182 (Doi:): 1401-1418.e18https://doi.org/10.1016/j.cell.2020.08.002Google Scholar,5Guo Qirui Zhao Yingchi Li Junhong Qin Chuan Wang Xiangxi Correspondence Fuping You. Induction of alarmin S100A8/A9 mediates activation of aberrant neutrophils in the pathogenesis of COVID-19.Cell Host Microbe. 2021; 29 (Doi:): 222-235.e4https://doi.org/10.1016/j.chom.2020.12.016Google Scholar. Recent studies, including two published in this journal, have subsequently proposed serum calprotectin as an early sensitive biomarker for predicting deterioration from COVID-19 in Emergency Departments (ED)6Bauer Wolfgang Diehl-Wiesenecker Eva Ulke Jannis Galtung Noa Havelka Aleksandra Hegel J.Kolja et al.Outcome prediction by serum calprotectin in patients with COVID-19 in the emergency department.J Infect. 2021; (Doi:): 84-123https://doi.org/10.1016/j.jinf.2020.11.016Google Scholar, 7Romualdo Luis García de Guadiana Mulero María Dolores Rodríguez Olivo Marta Hernández Rojas Carlos Rodríguez Arenas Verónica Ramos Morales Mercedes González et al.Circulating levels of GDF-15 and calprotectin for prediction of in-hospital mortality in COVID-19 patients: a case series.J Infect. 2021; 82 (Doi:): e40https://doi.org/10.1016/J.JINF.2020.08.010Google Scholar, 8Mahler M. Meroni P.L. Infantino M. Buhler K.A. Fritzler M.J. Circulating Calprotectin as a Biomarker of COVID-19 Severity.Expert Rev Clin Immunol. 2021; 17 (Doi:): 431-443https://doi.org/10.1080/1744666X.2021.1905526Google Scholar. Whether the utility of serum calprotectin extends to adult patients attending SDEC, and whether its addition to existing deterioration models improves prediction of deterioration is unknown. To determine this, from February to April 2021 we prospectively asked SDEC clinicians in Oxford University NHS Foundation Trust, UK, to order a pre-specified panel of biochemical blood tests through an electronic 'Careset' (EPR, Cerner Millenium) for all patients suspected of having COVID-19 based on symptomology or epidemiology. Selection of the Careset triggered automatic analysis of serum calprotectin using a particle enhanced turbidimetric assay (Gentian AS, Moss, Norway). Clinicians were blinded to calprotectin results, and laboratory staff blinded to COVID-19 status. We subsequently employed the Infections in Oxfordshire Research Database (IORD) to identify individuals and hospital episodes with serum calprotectin available on the Laboratory Information Management System, then extracted demographic, clinical, biochemical and outcome information stored on the electronic healthcare records in a structured and anonymised way for downstream analysis. IORD has Research Ethics Committee and Confidentiality Advisory Group approval (19/SC/0403, 19/CAG/0144) for use as a de-identified electronic research database9Vihta Karina Doris Stoesser Nicole Llewelyn Martin J. Quan T. Phuong Davies Tim Fawcett Nicola J. et al.Trends over time in Escherichia coli bloodstream infections, urinary tract infections, and antibiotic susceptibilities in Oxfordshire, UK, 1998–2016: a study of electronic health records.Lancet Infect Dis. 2018; 18 (Doi:): 1138-1149https://doi.org/10.1016/S1473-3099(18)30353-0Google Scholar. COVID-19 diagnosis was retrospectively defined as a composite of select internationally standardised diagnostic codes (using ICD10 codes Z208, Z861, J128, M358, Z115 and/or a positive PCR test for SARS-CoV2 during the patient encounter. We determined that a patient had deteriorated if they required application of NIV, were admitted onto ICU or died within four weeks of admission. Any remaining patients were censored at that point. All data analyses were undertaken in R (version 4.0.2). Out of 3280 patients reviewed in acute ambulatory care over the study period, 771 (23.5%) were suspected of having COVID-19, with serum calprotectin levels available within 48 h of presentation to hospital (Table 1). Of the 771, 222 (28.8%; 6.8% of all those reviewed) had a final diagnosis of COVID-19 and 25 (11.3%) of these patients reached the composite endpoint (18 died, 6 commenced on NIV and 2 admitted onto ICU, where one individual died after commencing on NIV).Table 1Characteristics of patients with calprotectin levels available at presentation to ambulatory care during the months of February to April 2021. Univariate P-values were calculated using the Mann-Whitney-U test for continuous variables and Fisher's Exact Test for nominal variables.CharacteristicAll(n = 771)COVID-19 diagnosis(n = 222)COVID-19 with no outcome(n = 197)COVID-19 with outcome(n = 25)Evidence of difference between COVID-19 groups (P)DemographicsAge at presentation in years64 (45–78)69 (48–81)68 (47–80)77 (58–89)*P<0.05.Female sex422 (55)111 (50)101 (51)10 (40)NSBMI27 (24–32)27 (24–32)28 (24–32)25 (23–31)NSCharlson comorbidity index3 (0–10)3 (0–10)3 (0–8)13 (4–19)⁎⁎⁎P<0.001; NA: not applicable.Index of multiple deprivation11 (7–17)11 (7–17)11 (7–17)8 (6–15)NSClinical measures at presentationSupplemental oxygen33 (4)18 (8)15 (8.0)3 (12.0)NSRespiratory rate, breaths/min18 (18–19)18 (17–19)18 (17–19)18 (18–19)NSOxygen saturation,%97 (95–98)97 (95–98)97 (95–98)95 (93–96)⁎⁎⁎P<0.001; NA: not applicable.Glasgow coma scale15 (15–15)15 (15–15)15 (15–15)15 (14–15)*P<0.05.OutcomesDeath47 (6)18 (8)–18 (72)NARequiring NIV6 (1)6 (3)–6 (24)NAICU Admission2 (1)2 (1)–2 (8)NAComposite outcome54 (7)25 (11)–25 (100)NABiomarkersNeutrophil count, x10×9/L5.3 (3.9–7.5)5.8 (4.4–8.5)5.7 (4.4–8.4)6.9 (4.9–9.6)NSLymphocytes count, x10×9/L1.5 (1.0–1.6)1.4 (0.9–2.0)1.4 (1.0–1.9)1.0 (0.7–1.5)*P<0.05.Urea, mmol/L5.1 (3.9–7.1)5.7 (4.2–7.7)5.5 (4.2–7.2)7.7 (5.2–13.9)⁎⁎P<0.01.C-reactive protein, mg/L6.0 (1.6–28.7)12.4 (3.5–72.8)10.4 (3.0–64.1)70.5 (38.8–165.6)⁎⁎⁎P<0.001; NA: not applicable.Calprotectin, mg/L1.9 (1.1–3.3)2.2 (1.3–4.1)2.1 (1.3–3.8)3.7 (1.7–5.7)NSContinuous variables are represented with median and IQR, nominal variables with frequency and column percentage (of valid cases).NS: non-significant,. P<0.05. P<0.01. P<0.001; NA: not applicable. Open table in a new tab Continuous variables are represented with median and IQR, nominal variables with frequency and column percentage (of valid cases). NS: non-significant,. Univariate associations with risk of deterioration were observed for several variables including Charlson comorbidity index (P = 8.1 × 10−5), oxygen saturation (P = 7.6 × 10−3), and C-reactive protein (P = 4.5 × 10−5), but not neutrophil count or calprotectin (Table 1). Calprotectin had a univariate area under the receiver operator characteristic curve (AUROC) estimate of 0.61 (95% confidence interval 0.48–0.74) compared to 0.76 (0.67–0.84) for CRP in patients with COVID-19 (Fig. 1A) with a similar pattern observed for all 771 individuals tested (AUROC 0.62 and 0.79 respectively). Use of CRP had a statistically greater capability of discriminating risk of deterioration compared to calprotectin in both analyses (P = 0.01). Testing correlation between measured biomarkers in the full dataset of 771 individuals, the highest correlation was observed between neutrophil count and calprotectin (rho=0.61) with a similar estimate observed between calprotectin and CRP (rho=0.58; Fig. 1B). In multivariate models, when used alongside CRP with age and sex, calprotectin led to only a marginal improvement in predicative capability. There was no incremental benefit when using all available data as part of a gold standard predictive model (Supplementary Table 1). We conclude that in this large cohort attending SDEC during a surge of COVID-19 in the UK, whilst serum calprotectin was found to be a potential predictor of deterioration, there was little evidence that it offered benefit over and above existing biomarkers including peripheral cell counts or CRP. Other studies investigating calprotectin as a potential predictor of adverse outcome include a German ED study that enroled 66 individuals with suspected COVID-19 where calprotectin was found to have a AUROC of 0.87, compared to 0.70 for CRP, for predicting multi-organ failure within 72 h6Bauer Wolfgang Diehl-Wiesenecker Eva Ulke Jannis Galtung Noa Havelka Aleksandra Hegel J.Kolja et al.Outcome prediction by serum calprotectin in patients with COVID-19 in the emergency department.J Infect. 2021; (Doi:): 84-123https://doi.org/10.1016/j.jinf.2020.11.016Google Scholar. Another Spanish ED study found estimates of 0.80 and 0.79 respectively for predicting death during admission7Romualdo Luis García de Guadiana Mulero María Dolores Rodríguez Olivo Marta Hernández Rojas Carlos Rodríguez Arenas Verónica Ramos Morales Mercedes González et al.Circulating levels of GDF-15 and calprotectin for prediction of in-hospital mortality in COVID-19 patients: a case series.J Infect. 2021; 82 (Doi:): e40https://doi.org/10.1016/J.JINF.2020.08.010Google Scholar. Thus, these reported estimates for CRP are similar to ours whereas our estimate for calprotectin is significantly lower. This discrepancy could be due to the timing of sampling in relationship to clinical deterioration4Silvin Aymeric Chapuis Nicolas Dunsmore Garett Goubet Anne Gaëlle Dubuisson Agathe Derosa Lisa et al.Elevated calprotectin and abnormal myeloid cell subsets discriminate severe from mild COVID-19.Cell. 2020; 182 (Doi:): 1401-1418.e18https://doi.org/10.1016/j.cell.2020.08.002Google Scholar. Equally, as neither calprotectin nor neutrophil count were associated with risk of deterioration in our SDEC cohort there is the possibility that calprotectin may be more helpful in patients presenting more unwell to ED. Although we were unable to collect some important variables such as duration of symptoms and standardised radiology results owing to the priority of anonymization, our double-blind prospective design using standardised clinical data available through electronic healthcare records with multivariable analyses reduces the risk of selection bias and offers an effective, pragmatic opportunity for the rapid assessment of other such biomarkers in the future. Our findings do not support the widespread uptake of serum calprotectin use in ambulatory adult patients to predict COVID-19 deterioration, but does support the ongoing use of biomarkers such as CRP alongside standard clinical assessment in this setting as well as for predicting deterioration from other respiratory disease in SDEC. Supplementary Table 1 Reagents for serum calprotectin measures were provided by Gentian AS. Gentian AS had no role in the design, performance or analysis of the study but reviewed the results and interpretation before presentation. All authors declare no conflicts of interest. We thank the clinicians and other allied health staff contributing to this study. This work uses data provided by patients and collected by the UK's National Health Service as part of their care and support. We thank all the people of Oxfordshire who contribute to the Infections in Oxfordshire Research Database and Jack Cregan for managing the data extracts. Research Database Team: L Butcher, H Boseley, C Crichton, DW Crook, D Eyre, O Freeman, J Gearing (community), R Harrington, K Jeffery, M Landray, A Pal, TEA Peto, TP Quan, J Robinson (community), J Sellors, B Shine, AS Walker, D Waller. Patient and Public Panel: G Blower, C Mancey, P McLoughlin, B Nichols. AJM is an Academic Clinical Lecturer supported by the National Institute for Health Research. IORD is supported by the Oxford NIHR Biomedical Research Centre (OxBRC, [grant number IS-BRC-1215–20008]). JCK is supported by a Wellcome Trust Investigator Award [grant number 204969/Z/16/Z] and the OxBRC.

Objectives We investigate determinants of SARS-CoV-2 anti-spike IgG responses in healthcare workers (HCWs) following one or two doses of Pfizer-BioNTech or Oxford-AstraZeneca vaccines. Methods HCWs participating in regular SARS-CoV-2 PCR and antibody testing were invited for serological testing prior to first and second vaccination, and 4 weeks post-vaccination if receiving a 12-week dosing interval. Quantitative post-vaccination anti-spike antibody responses were measured using the Abbott SARS-CoV-2 IgG II Quant assay (detection threshold: ≥50 AU/ml). We used multivariable logistic regression to identify predictors of seropositivity and generalised additive models to track antibody responses over time. Results Vaccine uptake was 80%, but less in lower-paid roles and Black, south Asian and minority ethnic groups. 3570/3610(98.9%) HCWs were seropositive >14 days post-first vaccination and prior to second vaccination, 2706/2720(99.5%) after Pfizer-BioNTech and 864/890(97.1%) following Oxford-AstraZeneca vaccines. Previously infected and younger HCWs were more likely to test seropositive post-first vaccination, with no evidence of differences by sex or ethnicity. All 470 HCWs tested >14 days after second vaccine were seropositive. Quantitative antibody responses were higher after previous infection: median(IQR) >21 days post-first Pfizer-BioNTech 14,604(7644-22,291) AU/ml vs. 1028(564-1985) AU/ml without prior infection (p<0.001). Oxford-AstraZeneca vaccine recipients had lower readings post-first dose compared to Pfizer-BioNTech, with and without previous infection, 10,095(5354-17,096) and 435(203-962) AU/ml respectively (both p<0.001 vs. Pfizer-BioNTech). Antibody responses post-second vaccination were similar to those after prior infection and one vaccine dose. Conclusions Vaccination leads to detectable anti-spike antibodies in nearly all adult HCWs. Whether differences in response impact vaccine efficacy needs further study.

BACKGROUND:Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunoglobulin G (IgG) antibody measurements can be used to estimate the proportion of a population exposed or infected and may be informative about the risk of future infection. Previous estimates of the duration of antibody responses vary. METHODS:We present 6 months of data from a longitudinal seroprevalence study of 3276 UK healthcare workers (HCWs). Serial measurements of SARS-CoV-2 anti-nucleocapsid and anti-spike IgG were obtained. Interval censored survival analysis was used to investigate the duration of detectable responses. Additionally, Bayesian mixed linear models were used to investigate anti-nucleocapsid waning. RESULTS:Anti-spike IgG levels remained stably detected after a positive result, for example, in 94% (95% credibility interval [CrI] 91-96%) of HCWs at 180 days. Anti-nucleocapsid IgG levels rose to a peak at 24 (95% CrI 19-31) days post first polymerase chain reaction (PCR)-positive test, before beginning to fall. Considering 452 anti-nucleocapsid seropositive HCWs over a median of 121 days from their maximum positive IgG titer, the mean estimated antibody half-life was 85 (95% CrI 81-90) days. Higher maximum observed anti-nucleocapsid titers were associated with longer estimated antibody half-lives. Increasing age, Asian ethnicity, and prior self-reported symptoms were independently associated with higher maximum anti-nucleocapsid levels and increasing age and a positive PCR test undertaken for symptoms with longer anti-nucleocapsid half-lives. CONCLUSIONS:SARS-CoV-2 anti-nucleocapsid antibodies wane within months and fall faster in younger adults and those without symptoms. However, anti-spike IgG remains stably detected. Ongoing longitudinal studies are required to track the long-term duration of antibody levels and their association with immunity to SARS-CoV-2 reinfection.

Background Natural and vaccine-induced immunity will play a key role in controlling the SARS-CoV-2 pandemic. SARS-CoV-2 variants have the potential to evade natural and vaccine-induced immunity. Methods In a longitudinal cohort study of healthcare workers (HCWs) in Oxfordshire, UK, we investigated the protection from symptomatic and asymptomatic PCR-confirmed SARS-CoV-2 infection conferred by vaccination (Pfizer-BioNTech BNT162b2, Oxford-AstraZeneca ChAdOx1 nCOV-19) and prior infection (determined using anti-spike antibody status), using Poisson regression adjusted for age, sex, temporal changes in incidence and role. We estimated protection conferred after one versus two vaccinations and from infections with the B.1.1.7 variant identified using whole genome sequencing. Results 13,109 HCWs participated; 8285 received the Pfizer-BioNTech vaccine (1407 two doses) and 2738 the Oxford-AstraZeneca vaccine (49 two doses). Compared to unvaccinated seronegative HCWs, natural immunity and two vaccination doses provided similar protection against symptomatic infection: no HCW vaccinated twice had symptomatic infection, and incidence was 98% lower in seropositive HCWs (adjusted incidence rate ratio 0.02 [95%CI <0.01-0.18]). Two vaccine doses or seropositivity reduced the incidence of any PCR-positive result with or without symptoms by 90% (0.10 [0.02-0.38]) and 85% (0.15 [0.08-0.26]) respectively. Single-dose vaccination reduced the incidence of symptomatic infection by 67% (0.33 [0.21-0.52]) and any PCR-positive result by 64% (0.36 [0.26-0.50]). There was no evidence of differences in immunity induced by natural infection and vaccination for infections with S-gene target failure and B.1.1.7. Conclusion Natural infection resulting in detectable anti-spike antibodies and two vaccine doses both provide robust protection against SARS-CoV-2 infection, including against the B.1.1.7 variant.

Background Thresholds for SARS-CoV-2 antibody assays have typically been determined using samples from symptomatic, often hospitalised, patients. In this setting the sensitivity and specificity of the best performing assays can both exceed 98%. However, antibody assay performance following mild infection is less clear. Methods We assessed quantitative IgG responses in a cohort of healthcare workers in Oxford, UK, with a high pre-test probability of Covid-19, in particular the 991/11,475(8.6%) who reported loss of smell/taste. We use anosmia/ageusia and other risk factors as probes for Covid-19 infection potentially undiagnosed by immunoassays by investigating their relationship with antibody readings either side of assay thresholds. Results The proportion of healthcare workers reporting anosmia/ageusia increased at antibody readings below diagnostic thresholds using an in-house ELISA ( n = 9324) and the Abbott Architect chemiluminescent microparticle immunoassay (CMIA; n = 11,324): 426/906 (47%) reported anosmia/ageusia with a positive ELISA, 59/449 (13.1%) with high-negative and 326/7969 (4.1%) with low-negative readings. Similarly, by CMIA, 518/1093 (47.4%) with a positive result reported anosmia/ageusia, 106/686 (15.5%) with a high-negative and 358/9563 (3.7%) with a low-negative result. Adjusting for the proportion of staff reporting anosmia/ageusia suggests the sensitivity of both assays in mild infection is lower than previously reported: Oxford ELISA 89.8% (95%CI 86.6–92.8%) and Abbott CMIA 79.3% (75.9–82.7%). Conclusion Following mild SARS-CoV-2 infection 10–30% of individuals may have negative immunoassay results. While lowered diagnostic thresholds may result in unacceptable specificity, our findings have implications for epidemiological analyses and result interpretation in individuals with a high pre-test probability. Samples from mild PCR-confirmed infections should be included in SARS-CoV-2 immunoassay evaluations.

SARS-CoV-2 IgG screening of 1,000 antenatal serum samples in the Oxford area, United Kingdom, between 14 April and 15 June 2020, yielded a 5.3% seroprevalence, mirroring contemporaneous regional data. Among the 53 positive samples, 39 showed in vitro neutralisation activity, correlating with IgG titre (Pearson’s correlation p<0.0001). While SARS-CoV-2 seroprevalence in pregnancy cohorts could potentially inform population surveillance, clinical correlates of infection and immunity in pregnancy, and antenatal epidemiology evolution over time need further study.

We conducted voluntary Covid-19 testing programmes for symptomatic and asymptomatic staff at a UK teaching hospital using naso-/oro-pharyngeal PCR testing and immunoassays for IgG antibodies. 1128/10,034 (11.2%) staff had evidence of Covid-19 at some time. Using questionnaire data provided on potential risk-factors, staff with a confirmed household contact were at greatest risk (adjusted odds ratio [aOR] 4.82 [95%CI 3.45–6.72]). Higher rates of Covid-19 were seen in staff working in Covid-19-facing areas (22.6% vs. 8.6% elsewhere) (aOR 2.47 [1.99–3.08]). Controlling for Covid-19-facing status, risks were heterogenous across the hospital, with higher rates in acute medicine (1.52 [1.07–2.16]) and sporadic outbreaks in areas with few or no Covid-19 patients. Covid-19 intensive care unit staff were relatively protected (0.44 [0.28–0.69]), likely by a bundle of PPE-related measures. Positive results were more likely in Black (1.66 [1.25–2.21]) and Asian (1.51 [1.28–1.77]) staff, independent of role or working location, and in porters and cleaners (2.06 [1.34–3.15]).

Background It is critical to understand whether infection with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) protects from subsequent reinfection. Methods We investigated the incidence of SARS-CoV-2 PCR-positive results in seropositive and seronegative healthcare workers (HCWs) attending asymptomatic and symptomatic staff testing at Oxford University Hospitals, UK. Baseline antibody status was determined using anti-spike and/or anti-nucleocapsid IgG assays and staff followed for up to 30 weeks. We used Poisson regression to estimate the relative incidence of PCR-positive results and new symptomatic infection by antibody status, accounting for age, gender and changes in incidence over time. Results A total of 12219 HCWs participated and had anti-spike IgG measured, 11052 were followed up after negative and 1246 after positive antibody results including 79 who seroconverted during follow up. 89 PCR-confirmed symptomatic infections occurred in seronegative individuals (0.46 cases per 10,000 days at risk) and no symptomatic infections in those with anti-spike antibodies. Additionally, 76 (0.40/10,000 days at risk) anti-spike IgG seronegative individuals had PCR-positive tests in asymptomatic screening, compared to 3 (0.21/10,000 days at risk) seropositive individuals. Overall, positive baseline anti-spike antibodies were associated with lower rates of PCR-positivity (with or without symptoms) (adjusted rate ratio 0.24 [95%CI 0.08-0.76, p=0.015]). Rate ratios were similar using anti-nucleocapsid IgG alone or combined with anti-spike IgG to determine baseline status. Conclusions Prior SARS-CoV-2 infection that generated antibody responses offered protection from reinfection for most people in the six months following infection. Further work is required to determine the long-term duration and correlates of post-infection immunity.

AbstractBackgroundSARS-CoV-2 IgG antibody measurements can be used to estimate the proportion of a population exposed or infected and may be informative about the risk of future infection. Previous estimates of the duration of antibody responses vary.MethodsWe present 6 months of data from a longitudinal seroprevalence study of 3217 UK healthcare workers (HCWs). Serial measurements of IgG antibodies to SARS-CoV-2 nucleocapsid were obtained. Bayesian mixed linear models were used to investigate antibody waning and associations with age, gender, ethnicity, previous symptoms and PCR results.ResultsIn this cohort of working age HCWs, antibody levels rose to a peak at 24 (95% credibility interval, CrI 19-31) days post-first positive PCR test, before beginning to fall. Considering 452 IgG seropositive HCWs over a median of 121 days (maximum 171 days) from their maximum positive IgG titre, the mean estimated antibody half-life was 85 (95%CrI, 81-90) days. The estimated mean time to loss of a positive antibody result was 137 (95%CrI 127-148) days. We observed variation between individuals; higher maximum observed IgG titres were associated with longer estimated antibody half-lives. Increasing age, Asian ethnicity and prior self-reported symptoms were independently associated with higher maximum antibody levels, and increasing age and a positive PCR test undertaken for symptoms with longer antibody half-lives.ConclusionIgG antibody levels to SARS-CoV-2 nucleocapsid wane within months, and faster in younger adults and those without symptoms. Ongoing longitudinal studies are required to track the long-term duration of antibody levels and their association with immunity to SARS-CoV-2 reinfection.SummarySerially measured SARS-CoV-2 anti-nucleocapsid IgG titres from 452 seropositive healthcare workers demonstrate levels fall by half in 85 days. From a peak result, detectable antibodies last a mean 137 days. Levels fall faster in younger adults and following asymptomatic infection.

Thresholds for SARS-CoV-2 antibody assays have typically been determined using samples from symptomatic, often hospitalised, patients. Assay performance following mild/asymptomatic infection is unclear. We assessed IgG responses in asymptomatic healthcare workers with a high pre-test probability of Covid-19, e.g. 807/9292(8.9%) reported loss of smell/taste. The proportion reporting anosmia/ageusia increased at antibody titres below diagnostic thresholds for both an in-house ELISA and the Abbott Architect chemiluminescent microparticle immunoassay (CMIA): 424/903(47%) reported anosmia/ageusia with a positive ELISA, 59/387(13.2%) with high-negative titres, and 324/7943(4.1%) with low-negative results. Adjusting for the proportion of staff reporting anosmia/ageusia suggests the sensitivity of both assays is lower than previously reported: Oxford ELISA 90.8% (95%CI 86.1-92.1%) and Abbott CMIA 80.9% (77.5-84.3%). However, the sensitivity may be lower if some anosmia/ageusia in those with low-negative titres is Covid-19-associated. Samples from individuals with mild/asymptomatic infection should be included in SARS-CoV-2 immunoassay evaluations. Reporting equivocal SARS-CoV-2 antibody results should be considered.

BACKGROUND:The relationship between the presence of antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the risk of subsequent reinfection remains unclear. METHODS:We investigated the incidence of SARS-CoV-2 infection confirmed by polymerase chain reaction (PCR) in seropositive and seronegative health care workers attending testing of asymptomatic and symptomatic staff at Oxford University Hospitals in the United Kingdom. Baseline antibody status was determined by anti-spike (primary analysis) and anti-nucleocapsid IgG assays, and staff members were followed for up to 31 weeks. We estimated the relative incidence of PCR-positive test results and new symptomatic infection according to antibody status, adjusting for age, participant-reported gender, and changes in incidence over time. RESULTS:A total of 12,541 health care workers participated and had anti-spike IgG measured; 11,364 were followed up after negative antibody results and 1265 after positive results, including 88 in whom seroconversion occurred during follow-up. A total of 223 anti-spike-seronegative health care workers had a positive PCR test (1.09 per 10,000 days at risk), 100 during screening while they were asymptomatic and 123 while symptomatic, whereas 2 anti-spike-seropositive health care workers had a positive PCR test (0.13 per 10,000 days at risk), and both workers were asymptomatic when tested (adjusted incidence rate ratio, 0.11; 95% confidence interval, 0.03 to 0.44; P = 0.002). There were no symptomatic infections in workers with anti-spike antibodies. Rate ratios were similar when the anti-nucleocapsid IgG assay was used alone or in combination with the anti-spike IgG assay to determine baseline status. CONCLUSIONS:The presence of anti-spike or anti-nucleocapsid IgG antibodies was associated with a substantially reduced risk of SARS-CoV-2 reinfection in the ensuing 6 months. (Funded by the U.K. Government Department of Health and Social Care and others.).

AbstractBackgroundPersonal protective equipment (PPE) and social distancing are designed to mitigate risk of occupational SARS-CoV-2 infection in hospitals. Why healthcare workers nevertheless remain at increased risk is uncertain.MethodsWe conducted voluntary Covid-19 testing programmes for symptomatic and asymptomatic staff at a UK teaching hospital using nasopharyngeal PCR testing and immunoassays for IgG antibodies. A positive result by either modality determined a composite outcome. Risk-factors for Covid-19 were investigated using multivariable logistic regression.Results1083/9809(11.0%) staff had evidence of Covid-19 at some time and provided data on potential risk-factors. Staff with a confirmed household contact were at greatest risk (adjusted odds ratio [aOR] 4.63 [95%CI 3.30-6.50]). Higher rates of Covid-19 were seen in staff working in Covid-19-facing areas (21.2% vs. 8.2% elsewhere) (aOR 2.49 [2.00-3.12]). Controlling for Covid-19-facing status, risks were heterogenous across the hospital, with higher rates in acute medicine (1.50 [1.05-2.15]) and sporadic outbreaks in areas with few or no Covid-19 patients. Covid-19 intensive care unit (ICU) staff were relatively protected (0.46 [0.29-0.72]). Positive results were more likely in Black (1.61 [1.20-2.16]) and Asian (1.58 [1.34-1.86]) staff, independent of role or working location, and in porters and cleaners (1.93 [1.25-2.97]). Contact tracing around asymptomatic staff did not lead to enhanced case identification. 24% of staff/patients remained PCR-positive at ≥6 weeks post-diagnosis.ConclusionsIncreased Covid-19 risk was seen in acute medicine, among Black and Asian staff, and porters and cleaners. A bundle of PPE-related interventions protected staff in ICU.