Different vaccine platforms result in distinct antibody responses to the same antigen in haemodialysis patients (preprint)

Generalised immune dysfunction in chronic kidney disease, especially in patients requiring haemodialysis (HD), significantly enhances the risk of severe infections. Moreover, vaccine-induced immunity is typically reduced in HD populations, but the full mechanisms behind this remain unclear. The SARS-CoV-2 pandemic provided an opportunity to examine the magnitude and functionality of antibody responses in HD patients to a previously unencountered antigen, Spike (S)-glycoprotein, after vaccination with different vaccine platforms (viral vector (VV); mRNA (mRV)). Here, we compared total and functional anti-S antibody responses (cross-variant neutralisation and complement binding) in 187 HD patients and 43 healthy controls 21-28 days after serial immunisation. After 2 doses of the same vaccine, HD patients had anti-S antibody levels and complement binding capacity comparable to controls. However, 2 doses of mRV induced greater polyfunctional antibody responses than VV, yet previous SARS-CoV-2 infection or an mRV boost after 2 doses of VV significantly enhanced antibody functionality in HD patients. Therefore, HD patients can generate near-normal, functional antigen-specific antibody responses following serial vaccination to a novel antigen, suggesting largely intact B cell memory. Encouragingly, exploiting immunological memory by using mRNA vaccines and boosting may improve the success of vaccination strategies in this vulnerable patient population.

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.

SARS-CoV-2 testing in the community: Testing positive samples with the TaqMan SARS-CoV-2 Mutation Panel to find variants in real-time (preprint)

Genome sequencing is a powerful tool for identifying SARS-CoV-2 variant lineages, however there can be limitations due to sequence drop-out when used to identify specific key mutations. Recently, Thermo Fisher Scientific have developed genotyping assays to help bridge the gap between testing capacity and sequencing capability to generate real-time genotyping results based on specific variants. Over a 6-week period during the months of April and May 2021, we set out to assess the Thermo Fisher TaqMan Mutation Panel Genotyping Assay, initially for three mutations of concern and then an additional two mutations of concern, against SARS-CoV-2 positive clinical samples and the corresponding COG-UK sequencing data. We demonstrate that genotyping is a powerful in-depth technique for identifying specific mutations, an excellent complement to genome sequencing and has real clinical health value potential allowing laboratories to report and action variants of concern much quicker.

S-variant SARS-CoV-2 is associated with significantly higher viral loads in samples tested by ThermoFisher TaqPath RT-QPCR (preprint)

Birmingham University Turnkey laboratory is part of the Lighthouse network responsible for testing clinical samples under the UK government ‘ Test & Trace’ scheme. Samples are analysed for the presence of SARS-CoV-2 in respiratory samples using the Thermofisher TaqPath RT-QPCR test, which is designed to co-amplify sections of three SARS-CoV-2 viral genes. Since more recent information became available regarding the presence of SARS-CoV-2 variants of concern (S-VoC), which can show a suboptimal profile in RT-QPCR tests such as the ThermoFisher TaqPath used at the majority of Lighthouse laboratories, we analysed recently published data for trends and significance of the S-gene ‘dropout’ variant. Results: showed that: the population of S-gene dropout samples had significantly lower median Ct values of ORF and N-gene targets compared to samples where S-gene was detected on a population basis, S-gene dropout samples clustered around very low Ct values for ORF and N targets linked Ct values for individual samples showed that a low Ct for ORF and N were clearly associated with an S-dropout characteristic when conservatively inferring relative viral load from Ct values, approximately 35% of S-dropout samples had high viral loads between 10 and 10,000-fold greater than 1 × 10 6 , compared to 10% of S-positive samples. This analysis suggests that patients whose samples exhibit the S-dropout profile in the TaqPath test are more likely to have high viral loads at the time of sampling. The relevance of this to epidemiological reports of fast spread of the SARS-CoV-2 in regions of the UK is discussed.

Extrapolation of United Kingdom Pillar 2 Care home Covid-19 test data to ascertain effectiveness of lateral flow testing in low prevalence settings (preprint)

Lateral flow devices are quickly being implemented for use in large scale population surveillance programs for SARS-CoV-2 infection in the United Kingdom. These programs have been piloted in city wide screening in the city of Liverpool, and are now being rolled out to support care home visits and the return home of University students for the Christmas break. Very little data exists comparing the performance of the UK lateral flow tests with gold standard PCR diagnostics, especially against comparable test populations such as the national Pillar 2 testing program in the United Kingdom. Here we utilise thousands of pillar 2 test data from our University of Birmingham test lab, and by extrapolation against the validate limit-of-detection of the lateral flow assay, provide a potential sensitivity for the test in a comparable low prevalence population captured in the pillar 2 program. Our data suggests the lateral flow assay should successfully capture around 85% of all PCR positive tests performed in our pillar 2 laboratory, and that a fully designed comparative study of lateral flow versus PCR testing is merited in a real life testing environment