COVID-19 vaccine design and vaccination rollout need to take into account a detailed understanding of antibody durability and cross-neutralizing potential against SARS-CoV-2 and emerging variants of concern (VOCs). Analyses of convalescent sera provide unique insights into antibody longevity and cross-neutralizing activity induced by variant spike proteins, which are putative vaccine candidates. Using sera from 38 individuals infected in wave 1, we show that cross-neutralizing activity can be detected up to 305 days pos onset of symptoms, although sera were less potent against B.1.1.7 (Alpha) and B1.351 (Beta). Over time, despite a reduction in overall neutralization activity, differences in sera neutralization potency against SARS-CoV-2 and the Alpha and Beta variants decreased, which suggests that continued antibody maturation improves tolerance to spike mutations. We also compared the cross-neutralizing activity of wave 1 sera with sera from individuals infected with the Alpha, the Beta or the B.1.617.2 (Delta) variants up to 79 days post onset of symptoms. While these sera neutralize the infecting VOC and parental virus to similar levels, cross-neutralization of different SARS-CoV-2 VOC lineages is reduced. These findings will inform the optimization of vaccines to protect against SARS-CoV-2 variants.

Background: Understanding of the true asymptomatic rate of infection of SARS-CoV-2 is currently limited, as is understanding of the population-based seroprevalence after the first wave of COVID-19 within the UK. The majority of data thus far come from hospitalised patients, with little focus on general population cases, or their symptoms. Methods: We undertook enzyme linked immunosorbent assay characterisation of IgM and IgG responses against SARS-CoV-2 spike glycoprotein and nucleocapsid protein of 431 unselected general-population participants of the TwinsUK cohort from SouthEast England, aged 19-86 (median age 48; 85% female). 382 participants completed prospective logging of 14 COVID-19 related symptoms via the COVID Symptom Study App, allowing consideration of serology alongside individual symptoms, and a predictive algorithm for estimated COVID-19 previously modelled on PCR positive individuals from a dataset of over 2 million. Findings: We demonstrated a seroprevalence of 12% (51 participants of 431). Of 48 seropositive individuals with full symptom data, nine (19%) were fully asymptomatic, and 16 (27%) were asymptomatic for core COVID-19 symptoms: fever, cough or anosmia. Specificity of anosmia for seropositivity was 95%, compared to 88% for fever cough and anosmia combined. 34 individuals in the cohort were predicted to be Covid-19 positive using the App algorithm, and of those, 18 (52%) were seropositive. Interpretation: Seroprevalence amongst adults from London and SouthEast England was 12%, and 19% of seropositive individuals with prospective symptom logging were fully asymptomatic throughout the study. Anosmia demonstrated the highest symptom specificity for SARS-CoV-2 antibody response.

There is a worldwide shortage of reagents to perform detection of SARS-CoV-2. Many clinical diagnostic laboratories rely on commercial platforms that provide integrated end-to-end solutions. While this provides established robust pipelines, there is a clear bottleneck in the supply of reagents given the current situation of extraordinary high demand. Some laboratories resort to implementing kit-free handling procedures, but many other small laboratories will not have the capacity to develop those and/or will perform manual handling of their samples. In order to provide multiple workflows for SARS-CoV-2 nucleic acid detection we compared several commercially available RNA extraction methods: QIAamp Viral RNA Mini Kit (QIAGEN), the recently developed RNAdvance Blood (Beckman) and Mag-Bind Viral DNA/RNA 96 Kit (Omega Bio-tek). We also compared different 1-step RT-qPCR Master Mix brands: TaqMan™ Fast Virus 1-Step Master Mix (ThermoFisher Scientific), qPCRBIO Probe 1-Step Go Lo-ROX (PCR Biosystems) and Luna® Universal Probe One-Step RT-qPCR Kit (NEB). We used the Centre for Disease Control (CDC) recommended primers that detect two regions of the viral N gene as well as those that detect the RdRP gene region as per Public Health England (PHE) guidelines (Charité/WHO/PHE). Our data show that the RNA extraction methods provide similar results. Amongst the qPCR reagents tested, TaqMan™ Fast Virus 1-Step Master Mix and Luna® Universal Probe One-Step RT-qPCR Kit proved most sensitive. The N1 and N2 primer-probes provide a more reliable detection than the RdRP_SARSr primer-probe set, particularly in samples with low viral titres. Importantly, we have implemented a protocol using heat inactivation and demonstrate that it has minimal impact on the sensitivity of the qPCR in clinical samples -potentially making SARS-CoV-2 testing portable to settings that do not have CL-3 facilities. In summary, we provide several testing pipelines that can be easily implemented in other laboratories and have made all our protocols and SOPs freely available at https://osf.io/uebvj/.