Breadth of neutralising antibody responses to SARS-CoV-2 variants of concern is augmented by vaccination following prior infection: studies in UK healthcare workers and immunodeficient patients

Approximately 75% of the UK population has received only one dose of a 2-dose COVID-19 vaccine regime in the face of circulating SARS-CoV-2 Variants of Concern (VOCs). We aimed to determine the levels of vaccine-induced neutralising antibodies to SARS-CoV-2 variants B.1.1.7, B.1.351 and P.1. To do so, we undertook a single-centre cross-sectional study of health care workers (HCWs) and outpatients with immunodeficiencies (IDP) based at the same critical care tertiary NHS Trust, following a single dose of either BNT162b2 or AZD1222 vaccines. Data revealed low neutralising antibodies (nAbs) in IDPs, with only 5% and 3% showing detectable neutralisation of B.1.1.7 and B.1.351, respectively. In contrast, healthy HCWs without a prior SARS-CoV-2 infection demonstrated a wide range of nAb titres post-vaccination with responses significantly lower than HCWs with prior SARS-CoV-2 infection. Neutralisation of VOCs with the E484K mutation (B.1.351 and P.1) were consistently lower in HCWs in the absence of evidence of prior SARS-CoV-2 infection (p<0.001). Notably, in vaccinated HCWs with prior SARS-CoV-2 infection, there was a significant increase of neutralising titres post-vaccination to all variants, compared to their pre-vaccination neutralisation titres. This underscores the importance of vaccination to boost neutralising antibody breadth to VOCs, and also provides support for the hypothesis that repeated immunisations will boost protective immunity in individuals without prior SARS-CoV-2 exposure.

Standardised, quantitative neutralisation responses to SARS-CoV-2 Variants of Concern by convalescent anti-sera from first wave infections of UK Health Care Workers and Patients

BackgroundThe rise of SARS-CoV-2 variants has made the pursuit to define correlates of protection more troublesome, despite the availability of the World Health Organisation (WHO) International Standard for anti-SARS-CoV-2 Immunoglobulin sera, a key reagent used to standardise laboratory findings into an international unitage. MethodsUsing pseudotyped virus, we examine the capacity of convalescent sera, from a well-defined cohort of healthcare workers (HCW) and Patients infected during the first wave from a national critical care centre in the UK to neutralise B.1.1.298, variants of interest (VOI) B.1.617.1 (Kappa), and four VOCs, B.1.1.7 (Alpha), B.1.351 (Beta), P.1 (Gamma) and B.1.617.2 (Delta), including the B.1.617.2 K417N, informally known as Delta Plus. We utilised the WHO International Standard for anti-SARS-CoV-2 Immunoglobulin to report neutralisation antibody levels in International Units per mL. FindingsOur data demonstrate a significant reduction in the ability of first wave convalescent sera to neutralise the VOCs. Patients and HCWs with more severe COVID-19 were found to have higher antibody titres and to neutralise the VOCs more effectively than individuals with milder symptoms. Using an estimated threshold for 50% protection, 54 IU/mL, we found most asymptomatic and mild cases did not produce titres above this threshold. InterpretationExpressing our data in IU/ml, we provide a benchmark pre-vaccine standardised dataset that compares disease severity with neutralising antibody titres. Our data may now be compared across multiple laboratories. The continued use and aggregation of standardised data will eventually assist in defining correlates of protection. FundingUKRI and NIHR; grant number G107217 Research in contextO_ST_ABSEvidence before this studyC_ST_ABSDuring the first wave outbreak, much focus was placed on the role of neutralising antibodies and titres generated upon infection to ancestral SARS-CoV-2. Due to the large amounts of different assays used to elucidate the antibody-mediated immunity and laboratory to laboratory, large amounts of invaluable data could not be directly compared in order to define a correlate of protection, due to variability in the results. The WHO International Standard for anti-SARS-CoV-2 Immunoglobulin sera was made in order to standardise future data so that comparisons may take place. Added value of this studyOur study compares the neutralisation capacity of sera from patients and healthcare workers (HCWs) from the ancestral strain of SARS-CoV-2 against new variants, including the current variants of concern in circulation. We also provide data in International Units per mL, a standardised unitage, for infected individuals that have a clinical severity score, allowing us to assess levels of neutralising antibodies across different severities of COVID-19 disease. By providing a method to calibrate most of the variants of concern so that the WHO International Standard for anti-SARS-CoV-2 Immunoglobulin reagent could be used to standardise our results, therefore making them comparable to other laboratories who also standardised their data in an identical manner. Implications of all the available evidenceContinual use and accumulation of standardised data would eventually lead to defining the correlates of protection against SARS-CoV-2. This could help to inform medical staff to identify which individuals would be a greater risk of a potential reinfection to SARS-CoV-2.

Towards Internationally standardised humoral Immune Correlates of Protection from SARS CoV 2 infection and COVID-19 disease

Precision monitoring of antibody responses during the COVID-19 pandemic is increasingly important during large scale vaccine rollout and rise in prevalence of Severe Acute Respiratory Syndrome-related Coronavirus-2 (SARS-CoV-2) variants of concern (VOC). Equally important is defining Correlates of Protection (CoP) for SARS-CoV-2 infection and COVID-19 disease. Data from epidemiological studies and vaccine trials identified virus neutralising antibodies (Nab) and SARS-CoV-2 antigen-specific (notably RBD, and S) binding antibodies as candidate CoP. In this study, we used the World Health Organisation (WHO) international standard to benchmark neutralising antibody responses and a large panel of binding antibody assays to compare convalescent sera obtained from: a) COVID-19 patients; b) SARS-CoV-2 seropositive healthcare workers (HCW) and c) seronegative HCW. The ultimate aim of this study, was to identify biomarkers of humoral immunity that could be used as candidate CoP in internationally accepted unitage. Whenever suitable, the antibody levels of the samples studied were expressed in International Units (INU) for virus neutralisation assays or International Binding Antibody Units (BAU) for ELISA tests. In this work we used commercial and non-commercial antibody binding assays; a lateral flow test for detection of SARS-CoV-2-specific IgG / IgM; a high throughput multiplexed particle flow cytometry assay for SARS-CoV-2 Spike (S), Nucleocapsid (N) and Receptor Binding Domain (RBD) proteins); a multiplex antigen semi-automated immuno-blotting assay measuring IgM, IgA and IgG; a pseudotyped microneutralisation test (pMN) and electroporation-dependent neutralisation assay (EDNA). Our results indicate that overall, severe COVID-19 patients showed statistically significantly higher levels of SARS-CoV-2-specific neutralising antibodies (average 1029 IU/ml) than those observed in seropositive HCW with mild or asymptomatic infections (379 IU/ml) and that clinical severity scoring, based on WHO guidelines was tightly correlated with neutralisation and RBD / S binding assays. In addition, there was a positive correlation between severity, N-antibody assays and intracellular virus neutralisation.