The effect of pH on the structure of Bluetongue virus VP5.

The unenveloped Bluetongue virus capsid comprises several structural layers, the inner two comprising a core, which assembles before addition of the outer proteins, VP2 and VP5. Two symmetric trimers of VP5 fit like pegs into two distinct pits on the core and undergo pH conformational changes in the context of the virus, associated with cell entry. Here we show that in isolation VP5 alone undergoes essentially the same changes with pH and confirm a helical transition, indicating that VP5 is a motor during cell entry. In the absence of VP5 the two pits on the core differ from each other, presumably due to the asymmetric underlying structure of VP3, the innermost capsid protein. On insertion of VP5 these pits become closely similar and remain similar at low pH whilst VP5 is present. This natural asymmetry presumably destabilises the attachment of VP5, facilitating ejection upon low pH, membrane penetration and cell entry.

Structural comparison of typical and atypical E2 pestivirus glycoproteins.

Pestiviruses, within the family Flaviviridae, are economically important viruses of livestock. In recent years, new pestiviruses have been reported in domestic animals and non-cloven-hoofed animals. Among them, atypical porcine pestivirus (APPV) and Norway rat pestivirus (NRPV) have relatively little sequence conservation in their surface glycoprotein E2. Despite E2 being the main target for neutralizing antibodies and necessary for cell attachment and viral fusion, the mechanism of viral entry remains elusive. To gain further insights into the pestivirus E2 mechanism of action and to assess its diversity within the genus, we report X-ray structures of the pestivirus E2 proteins from APPV and NRPV. Despite the highly divergent structures, both are able to dimerize through their C-terminal domain and contain a solvent-exposed ß-hairpin reported to be involved in host receptor binding. Functional analysis of this ß-hairpin in the context of BVDV revealed its ability to rescue viral infectivity.

Concerted deletions eliminate a neutralizing supersite in SARS-CoV-2 BA.2.87.1 spike.

BA.2.87.1 represents a major shift in the BA.2 lineage of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is unusual in having two lengthy deletions of polypeptide in the spike (S) protein, one of which removes a beta-strand. Here we investigate its neutralization by a variety of sera from infected and vaccinated individuals and determine its spike (S) ectodomain structure. The BA.2.87.1 receptor binding domain (RBD) is structurally conserved and the RBDs are tightly packed in an "all-down" conformation with a small rotation relative to the trimer axis as compared to the closest previously observed conformation. The N-terminal domain (NTD) maintains a remarkably similar structure overall; however, the rearrangements resulting from the deletions essentially destroy the so-called supersite epitope and eliminate one glycan site, while a mutation creates an additional glycan site, effectively shielding another NTD epitope. BA.2.87.1 is relatively easily neutralized but acquisition of additional mutations in the RBD could increase antibody escape allowing it to become a dominant sub-lineage.

The SARS-CoV-2 neutralizing antibody response to SD1 and its evasion by BA.2.86.

Under pressure from neutralising antibodies induced by vaccination or infection the SARS-CoV-2 spike gene has become a hotspot for evolutionary change, leading to the failure of all mAbs developed for clinical use. Most potent antibodies bind to the receptor binding domain which has become heavily mutated. Here we study responses to a conserved epitope in sub-domain-1 (SD1) of spike which have become more prominent because of mutational escape from antibodies directed to the receptor binding domain. Some SD1 reactive mAbs show potent and broad neutralization of SARS-CoV-2 variants. We structurally map the dominant SD1 epitope and provide a mechanism of action by blocking interaction with ACE2. Mutations in SD1 have not been sustained to date, but one, E554K, leads to escape from mAbs. This mutation has now emerged in several sublineages including BA.2.86, reflecting selection pressure on the virus exerted by the increasing prominence of the anti-SD1 response.

Emerging variants develop total escape from potent monoclonal antibodies induced by BA.4/5 infection.

The rapid evolution of SARS-CoV-2 is driven in part by a need to evade the antibody response in the face of high levels of immunity. Here, we isolate spike (S) binding monoclonal antibodies (mAbs) from vaccinees who suffered vaccine break-through infections with Omicron sub lineages BA.4 or BA.5. Twenty eight potent antibodies are isolated and characterised functionally, and in some cases structurally. Since the emergence of BA.4/5, SARS-CoV-2 has continued to accrue mutations in the S protein, to understand this we characterize neutralization of a large panel of variants and demonstrate a steady attrition of neutralization by the panel of BA.4/5 mAbs culminating in total loss of function with recent XBB.1.5.70 variants containing the so-called 'FLip' mutations at positions 455 and 456. Interestingly, activity of some mAbs is regained on the recently reported variant BA.2.86.

Southeast Asia initiative to combat SARS-CoV-2 variants (SEACOVARIANTS) consortium.

A strong and effective COVID-19 and future pandemic responses rely on global efforts to carry out surveillance of infections and emerging SARS-CoV-2 variants and to act accordingly in real time. Many countries in Southeast Asia lack capacity to determine the potential threat of new variants, or other emerging infections. Funded by Wellcome, the Southeast Asia initiative to combat SARS-CoV-2 variants (SEACOVARIANTS) consortium aims to develop and apply a multidisciplinary research platform in Southeast Asia (SEA) for rapid assessment of the biological significance of SARS-CoV-2 variants, thereby informing coordinated local, regional and global responses to the COVID-19 pandemic. Our proposal is delivered by the Vietnam and Thailand Wellcome Africa Asia Programmes, bringing together a multidisciplinary team in Indonesia, Thailand and Vietnam with partners in Singapore, the UK and the USA. Herein we outline five work packages to deliver strengthened regional scientific capacity that can be rapidly deployed for future outbreak responses.

Our project strengthens local scientific capacity in South East Asia (SEA) and therefore enables the rapid assessment of SARS-CoV-2 variants as they emerge within the region. While COVID-19 remains a global pandemic, future emerging infections caused by a novel virus is an inevitable event, with SEA being a global hot-spot for pathogen emergence. Consequently, the research capacity built, the scientists trained and the research network formed as part of this project will lay the foundation for future locally-led outbreak responses. Our project will demonstrate that novel research platforms can be set up in other low and middle income countries to address the unprecedented challenges presented by emerging infections.

Improving the representativeness of UK's national COVID-19 Infection Survey through spatio-temporal regression and post-stratification.

Population-representative estimates of SARS-CoV-2 infection prevalence and antibody levels in specific geographic areas at different time points are needed to optimise policy responses. However, even population-wide surveys are potentially impacted by biases arising from differences in participation rates across key groups. Here, we used spatio-temporal regression and post-stratification models to UK's national COVID-19 Infection Survey (CIS) to obtain representative estimates of PCR positivity (6,496,052 tests) and antibody prevalence (1,941,333 tests) for different regions, ages and ethnicities (7-December-2020 to 4-May-2022). Not accounting for vaccination status through post-stratification led to small underestimation of PCR positivity, but more substantial overestimations of antibody levels in the population (up to 21 percentage points), particularly in groups with low vaccine uptake in the general population. There was marked variation in the relative contribution of different areas and age-groups to each wave. Future analyses of infectious disease surveys should take into account major drivers of outcomes of interest that may also influence participation, with vaccination being an important factor to consider.

A structure-function analysis shows SARS-CoV-2 BA.2.86 balances antibody escape and ACE2 affinity.

BA.2.86, a recently described sublineage of SARS-CoV-2 Omicron, contains many mutations in the spike gene. It appears to have originated from BA.2 and is distinct from the XBB variants responsible for many infections in 2023. The global spread and plethora of mutations in BA.2.86 has caused concern that it may possess greater immune-evasive potential, leading to a new wave of infection. Here, we examine the ability of BA.2.86 to evade the antibody response to infection using a panel of vaccinated or naturally infected sera and find that it shows marginally less immune evasion than XBB.1.5. We locate BA.2.86 in the antigenic landscape of recent variants and look at its ability to escape panels of potent monoclonal antibodies generated against contemporary SARS-CoV-2 infections. We demonstrate, and provide a structural explanation for, increased affinity of BA.2.86 to ACE2, which may increase transmissibility.

Immunogenicity of Abdala COVID-19 vaccine in Vietnamese people after primary and booster vaccinations: a prospective observational study in Vietnam.

OBJECTIVES: We studied the immunogenicity after primary and booster vaccinations of Abdala COVID-19 vaccine, a receptor binding domain protein subunit vaccine, in Vietnamese people by determining the level of neutralization and cross-neutralization activities against the ancestral SARS-CoV-2 and its variants, and SARS-CoV-1. METHODS: We performed a prospective observational study, enrolling adults aged 19-59 years in Dong Thap province, southern Vietnam, and collected blood samples from baseline until 4 weeks post booster dose. We measured anti-nucleocapsid, anti-spike and neutralizing antibodies against SARS-CoV-2, and assessed the cross-neutralization against 14 SARS-CoV-2 variants, and SARS-CoV-1. Complementary antibody data came from Vietnamese healthcare workers fully vaccinated with ChAdOx1-S. RESULTS: After primary vaccination, anti-spike antibody and neutralizing antibodies were detectable in 98.4% and 87% of 251 study participants, respectively, with neutralizing antibody titers similar to that induced by ChAdOx1-S vaccine. Antibody responses after a homologous (Abdala COVID-19) or heterologous (mRNA BNT162b2) booster could neutralize 14 SARS-CoV-2 variants (including Omicron), and SARS-CoV-1. CONCLUSIONS: Abdala COVID-19 vaccine is immunogenic in Vietnamese people. Enhanced antibody response after a booster dose could cross-neutralize 14 SARS-CoV-2 variants and SARS-CoV-1. Our results have added to the growing body of knowledge about the contribution of protein subunit vaccine platforms to pandemic control.