Hematological ratios in coronavirus disease 2019 patients with and without invasive mechanical ventilation.

Patients with the most severe form of coronavirus disease 2019 (COVID-19) often require invasive ventilation. Determining the best moment to intubate a COVID-19 patient is complex decision and can result in important consequences for the patient. Therefore, markers that could aid in clinical decision-making such as hematological indices are highly useful. These markers are easy to calculate, do not generate extra costs for the laboratory, and are readily implemented in routine practice. Thus, this study aimed to investigate differences in the ratios calculated from the hemogram between patients with and without the need for invasive mechanical ventilation (IMV) and a control group. This was an observational retrospective analysis of 212 patients with COVID-19 that were hospitalized between April 1, 2020 and March 31, 2021 who were stratified as IMV (n = 129) or did not require invasive mechanical ventilation (NIMV) (n = 83). A control group of 198 healthy individuals was also included. From the first hemogram of each patient performed after admission, the neutrophil-to-lymphocyte ratio (NLR), the derived NLR (d-NLR), the lymphocyte-to-monocyte ratio, the platelet-to-lymphocyte ratio, the neutrophil-to-platelet ratio (NPR), and the systemic immune-inflammation index (SII) were calculated. All hematological ratios exhibited significant differences between the control group and COVID-19 patients. NLR, d-NLR, SII, and NPR were higher in the IMV group than they were in the NIMV group. The hematological indices addressed in this study demonstrated high potential for use as auxiliaries in clinical decision-making regarding the need for IMV.

SARS-CoV-2 Omicron spike mediated immune escape, infectivity and cell-cell fusion (preprint)

The Omicron variant emerged in southern Africa in late 2021 and is characterised by multiple spike mutations across all spike domains. Here we show that the Omicron spike confers very significant evasion of vaccine elicited neutralising antibodies that is more pronounced for ChAdOx-1 adenovirus vectored vaccine versus BNT162b2 mRNA vaccine. Indeed neutralisation of Omicron was not detectable for the majority of individuals who had received two doses of ChAdOx-1. Third dose mRNA vaccination rescues neutralisation in the short term. Despite three mutations predicted to favour spike S1/S2 cleavage, observed cleavage efficiency is lower than for wild type Wuhan-1 D614G and Delta. We demonstrate significantly lower infectivity of lung organoids and Calu-3 lung cells expressing endogenous levels of ACE2 and TMPRSS2 but similar infection as compared to Delta when using H1299 lung epithelial cells. Importantly, fusogenicity of the Omicron spike is impaired, leading to marked reduction in syncitia formation. These observations indicate that Omicron has gained immune evasion properties whilst possibly modulating properties associated with replication and pathogenicity.

SARS-CoV-2 B.1.617.2 Delta variant emergence and vaccine breakthrough (preprint)

The SARS-CoV-2 B.1.617.2 (Delta) variant was first identified in the state of Maharashtra in late 2020 and has spread throughout India, displacing the B.1.1.7 (Alpha) variant and other pre-existing lineages. Mathematical modelling indicates that the growth advantage is most likely explained by a combination of increased transmissibility and immune evasion. Indeed in vitro, the delta variant is less sensitive to neutralising antibodies in sera from recovered individuals, with higher replication efficiency as compared to the Alpha variant. In an analysis of vaccine breakthrough in over 100 healthcare workers across three centres in India, the Delta variant not only dominates vaccine-breakthrough infections with higher respiratory viral loads compared to non-delta infections (Ct value of 16.5 versus 19), but also generates greater transmission between HCW as compared to B.1.1.7 or B.1.617.1 (p=0.02). In vitro, the Delta variant shows 8 fold approximately reduced sensitivity to vaccine-elicited antibodies compared to wild type Wuhan-1 bearing D614G. Serum neutralising titres against the SARS-CoV-2 Delta variant were significantly lower in participants vaccinated with ChadOx-1 as compared to BNT162b2 (GMT 3372 versus 654, p<0001). These combined epidemiological and in vitro data indicate that the dominance of the Delta variant in India has been most likely driven by a combination of evasion of neutralising antibodies in previously infected individuals and increased virus infectivity. Whilst severe disease in fully vaccinated HCW was rare, breakthrough transmission clusters in hospitals associated with the Delta variant are concerning and indicate that infection control measures need continue in the post-vaccination era.

Age-related heterogeneity in Neutralising antibody responses to SARS-CoV-2 following BNT162b2 vaccination (preprint)

Two dose mRNA vaccination provides excellent protection against SARS-CoV-2. However, there are few data on vaccine efficacy in elderly individuals above the age of 801. Additionally, new variants of concern (VOC) with reduced sensitivity to neutralising antibodies have raised fears for vulnerable groups. Here we assessed humoral and cellular immune responses following vaccination with mRNA vaccine BNT162b22 in elderly participants prospectively recruited from the community and younger health care workers. Median age was 72 years and 51% were females amongst 140 participants. Neutralising antibody responses after the first vaccine dose diminished with increasing age, with a marked drop in participants over 80 years old. Sera from participants below and above 80 showed significantly lower neutralisation potency against B.1.1.7, B.1.351 and P.1. variants of concern as compared to wild type. Those over 80 were more likely to lack any neutralisation against VOC compared to younger participants following first dose. The adjusted odds ratio for inadequate neutralisation activity against the B.1.1.7, P.1 and B.1.351 variant in the older versus younger age group was 4.3 (95% CI 2.0-9.3, p<0.001), 6.7 (95% CI 1.7-26.3, p=0.008) and 1.7 (95% CI 0.5-5.7, p=0.41). Binding IgG and IgA antibodies were lower in the elderly, as was the frequency of SARS-CoV-2 Spike specific B-memory cells. We observed a trend towards lower somatic hypermutation in participants with suboptimal neutralisation, and elderly participants demonstrated clear reduction in class switched somatic hypermutation, driven by the IgA1/2 isotype. SARS-CoV-2 Spike specific T-cell IFN{gamma} and IL-2 responses fell with increasing age, and both cytokines were secreted primarily by CD4 T cells. We conclude that the elderly are a high risk population that warrant specific measures in order to mitigate against vaccine failure, particularly where variants of concern are circulating.

SARS-CoV-2 B.1.1.7 escape from mRNA vaccine-elicited neutralizing antibodies (preprint)

SARS-CoV-2 transmission is uncontrolled in many parts of the world, compounded in some areas by higher transmission potential of the B1.1.7 variant now seen in 50 countries. It is unclear whether responses to SARS-CoV-2 vaccines based on the prototypic strain will be impacted by mutations found in B.1.1.7. Here we assessed immune responses following vaccination with mRNA-based vaccine BNT162b2. We measured neutralising antibody responses following a single immunization using pseudoviruses expressing the wild-type Spike protein or the 8 mutations found in the B.1.1.7 Spike protein. The vaccine sera exhibited a broad range of neutralizing titres against the wild-type pseudoviruses (<1:4 to 3449) that were reduced against B.1.1.7 variant by 3.85 fold (IQR 2.68-5.28). This reduction was also evident in sera from some convalescent patients. Decreased B.1.1.7 neutralization was also observed with monoclonal antibodies targeting the N-terminal domain (9 out of 10), the Receptor Binding Motif (RBM) (5 outof 29), but not in neutralizing mAbs binding outside the RBM. Introduction of the E484K mutation in a B.1.1.7 background led to a further loss of neutralizing activity by vaccine-elicited antibodies over that conferred by the B.1.1.7 mutations alone. Further work is needed to establish the impact of these observations on protective vaccine efficacy in the context of the evolving B.1.1.7 lineage that will likely acquire E484K.

Impact of SARS-CoV-2 B.1.1.7 Spike variant on neutralisation potency of sera from individuals vaccinated with Pfizer vaccine BNT162b2 (preprint)

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) transmission is uncontrolled in many parts of the world, compounded in some areas by higher transmission potential of the B1.1.7 variant now seen in 50 countries. It is unclear whether responses to SARS-CoV-2 vaccines based on the prototypic strain will be impacted by mutations found in B.1.1.7. Here we assessed immune responses following vaccination with mRNA-based vaccine BNT162b2. We measured neutralising antibody responses following a single immunization using pseudoviruses expressing the wild-type Spike protein or the 8 amino acid mutations found in the B.1.1.7 spike protein. The vaccine sera exhibited a broad range of neutralising titres against the wild-type pseudoviruses that were modestly reduced against B.1.1.7 variant. This reduction was also evident in sera from some convalescent patients. Decreased B.1.1.7 neutralisation was also observed with monoclonal antibodies targeting the N-terminal domain (9 out of 10), the Receptor Binding Motif (RBM) (5 out of 31), but not in neutralising mAbs binding outside the RBM. Introduction of the E484K mutation in a B.1.1.7 background to reflect newly emerging viruses in the UK led to a more substantial loss of neutralising activity by vaccine-elicited antibodies and mAbs (19 out of 31) over that conferred by the B.1.1.7 mutations alone. E484K emergence on a B.1.1.7 background represents a threat to the vaccine BNT162b.

Decomposing the sources of SARS-CoV-2 fitness variation in the United States (preprint)

The fitness of a pathogen is composite phenotype determined by many different factors influencing growth rates both within and between hosts. Determining what factors shape fitness at the host population-level is especially challenging because both intrinsic factors like pathogen genetics and extrinsic factors such as host behaviour influence between-host transmission potential. These challenges have been highlighted by controversy surrounding the population-level fitness effects of mutations in the SARS-CoV-2 genome and their relative importance when compared against non-genetic factors shaping transmission dynamics. Building upon phylodynamic birth-death models, we develop a new framework to learn how hundreds of genetic and non-genetic factors have shaped the fitness of SARS-CoV-2. We estimate the fitness effects of all amino acid variants and several structural variants that have circulated in the United States between February and September 2020 from viral phylogenies. We also estimate how much fitness variation among pathogen lineages is attributable to genetic versus non-genetic factors such as spatial heterogeneity in transmission rates. Up to September 2020, most fitness variation between lineages can be explained by background spatial heterogeneity in transmission rates across geographic regions. Furthermore, no genetic variant including the Spike D614G mutation has had a significant effect on population-level fitness. Instead, the rapid increase in the frequency of the Spike D614G can be explained by the variant having a spatial transmission advantage due to first establishing in regions with higher transmission rates during the earliest stages of the pandemic.

Recurrent emergence and transmission of a SARS-CoV-2 Spike deletion ΔH69/V70 (preprint)

SARS-CoV-2 amino acid replacements in the receptor binding domain (RBD) occur relatively frequently and some have a consequence for immune recognition. Here we report recurrent emergence and significant onward transmission of a six-nucleotide out of frame deletion in the S gene, which results in loss of two amino acids: H69 and V70. We report that in human infections {Delta}H69/V70 often co-occurs with the receptor binding motif amino acid replacements N501Y, N439K and Y453F, and in the latter two cases has followed the RBD mutation. One of the {Delta}H69/V70+ N501Y lineages, now known as B.1.1.7, has undergone rapid expansion and includes eight S gene mutations: RBD (N501Y and A570D), S1 ({Delta}H69/V70 and {Delta}144) and S2 (P681H, T716I, S982A and D1118H). In vitro, we show that {Delta}H69/V70 does not reduce serum neutralisation across multiple convalescent sera. However, {Delta}H69/V70 increases infectivity and is associated with increased incorporation of cleaved spike into virions. {Delta}H69/V70 is able to compensate for small infectivity defects induced by RBD mutations N501Y, N439K and Y453F. In addition, replacement of H69 and V70 residues in the B.1.1.7 spike reduces its infectivity and spike mediated cell-cell fusion. Based on our data {Delta}H69/V70 likely acts as a permissive mutation that allows acquisition of otherwise deleterious immune escape mutations. Enhanced surveillance for the {Delta}H69/V70 deletion with and without RBD mutations should be considered as a global priority not only as a marker for the B.1.1.7 variant, but potentially also for other emerging variants of concern. Vaccines designed to target the deleted spike protein could mitigate against its emergence as increased selective forces from immunity and vaccines increase globally. HighlightsO_LI{Delta}H69/V70 is present in at least 28 SARS-CoV-2 lineages C_LIO_LI{Delta}H69/V70 does not confer escape from convalescent sera C_LIO_LI{Delta}H69/V70 increases spike infectivity and compensates for RBD mutations C_LIO_LI{Delta}H69/V70 is associated with greater spike cleavage C_LIO_LIB.1.1.7 requires {Delta}H69/V70 for optimal spike cleavage and infectivity C_LI

The Potential for SARS-CoV-2 to Evade Both Natural and Vaccine-induced Immunity (preprint)

SARS-CoV-2 attaches to the surface of susceptible cells through extensive interactions between the receptor binding domain (RBD) of its spike protein and angiotensin converting enzyme type 2 (ACE2) anchored in cell membranes. To investigate whether naturally occurring mutations in the spike protein are able to prevent antibody binding, yet while maintaining the ability to bind ACE2 and viral infectivity, mutations in the spike protein identified in cases of human infection were mapped to the crystallographically-determined interfaces between the spike protein and ACE2 (PDB entry 6M0J), antibody CC12.1 (PDB entry 6XC2), and antibody P2B-2F6 (PDB entry 7BWJ). Both antibody binding interfaces partially overlap with the ACE2 binding interface. Among 16 mutations that map to the RBD:CC12.1 interface, 11 are likely to disrupt CC12.1 binding but not ACE2 binding. Among 12 mutations that map to the RBD:P2B-2F6 interface, 8 are likely to disrupt P2B-2F6 binding but not ACE2 binding. As expected, none of the mutations observed to date appear likely to disrupt the RBD:ACE2 interface. We conclude that SARS-CoV-2 with mutated forms of the spike protein may retain the ability to bind ACE2 while evading recognition by antibodies that arise in response to the original wild-type form of the spike protein. It seems likely that immune evasion will be possible regardless of whether the spike protein was encountered in the form of infectious virus, or as the immunogen in a vaccine. Therefore, it also seems likely that reinfection with a variant strain of SARS-CoV-2 may occur among people who recover from Covid-19, and that vaccines with the ability to generate antibodies against multiple variant forms of the spike protein will be necessary to protect against variant forms of SARS-CoV-2 that are already circulating in the human population.