Persistence of a SARS-CoV-2 variant with a frameshifting deletion for the duration of a major outbreak (preprint)

Australia experienced widespread COVID-19 outbreaks from infection with the SARS-CoV-2 Delta variant between June 2021 and February 2022. Whole-genome sequencing of virus from an early case revealed a sub-consensus level of sequencing reads supporting a 17-nucleotide frameshift-inducing deletion in ORF7a that truncated the peptide sequence. The variant rapidly became represented at the consensus level (Delta-ORF7a{Delta}17del) in most of the outbreak cases in Australia. Retrospective analysis of ORF7a deletions in all GISAID clade GK Delta genomes showed that of 4,018,216 genomes, 134,751 (~3.35%) possessed a deletion in ORF7a, with the ORF7a{Delta}17del mutation by far the most common. Approximately 99.05% of Delta-ORF7a{Delta}17del genomes on GISAID originated from the Australian Delta outbreak, and comprised 87% of genomes in the outbreak. In vitro comparison of lineages in cell culture showed a significantly greater proportion of cells were infected with Delta-ORF7a{Delta}17del than with a contemporaneous Delta variant without ORF7a{Delta}17del (Delta-ORF7aintact), and the proportion was also measurably higher than an early SARS-CoV-2 strain (A.2.2). These results showed that Delta-ORF7a{Delta}17del potentially has a slight growth advantage compared to Delta-ORF7aintact. Delta-ORF7a{Delta}17del viruses still produced ORF7a protein, but significantly less than A.2.2, in a different cellular distribution with a more diffuse expression throughout the cytoplasm of infected cells. These data suggest that the proliferation of Delta-ORF7a{Delta}17del genomes during the Australian Delta outbreak was likely not a result of an intrinsic benefit of the ORF7a{Delta}17del mutation, but rather a chance founder effect. Nonetheless, the abundance of different ORF7a deletions in genomes worldwide suggests these have some benefit to virus transmission. IMPORTANCE Deletions in the ORF7a region of SARS-CoV-2 have been noted since early in the COVID-19 pandemic, but are generally reported as transient mutations that are quickly lost in the population. Consequently, ORF7a deletions are considered disadvantageous to the virus through possible loss-of-function effects. In constrast to these earlier reports, we present the first report of a SARS-CoV-2 variant with an ORF7a deletion that dominated for the entirety of a protracted outbreak, and found no associated fitness disadvantage or advantage in cell culture. The relatively common rise and fall of ORF7a deletion variants over time likely represent chance founder events followed by proliferation until a more fit variant(s) is introduced to the population. Our global clade-level survey of ORF7a deletions will be a useful resource for future studies into this gene region.

Rapid isolation and resolution immune evasion and viral fitness across contemporary SARS-CoV-2 variants (preprint)

From late 2020 the world observed the rapid emergence of many distinct SARS-CoV-2 variants. At the same time, pandemic responses coalesced into significant global vaccine roll-out that have now significantly lowered Covid-19 hospital and mortality rates in the developed world. Over this period, we developed a rapid platform (R-20) for viral isolation and characterisation using primary remnant diagnostic swabs. This combined with quarantine testing and genomics surveillance, enabled the rapid isolation and characterisation of all major SARS-CoV-2 variants (all variants of concern and 6 variants of interest) globally with a 4-month period. This platform facilitated viral variant isolation and enabled rapid resolution of variant phenotype by allowing determining end point viral titers from primary nasopharyngeal swabs and through ranking of evasion of neutralising antibodies. In late 2021, when the Delta variant was dominating, Omicron rapidly emerged. Using this platform, we isolated and tested the first cases of this variant within Australia. In this setting we observed Omicron to diverge from other variants at two levels: Firstly, it ranks at the mots evasive to neutralisation antibodies compared to all VOCs and major VUIs. Secondly, it no longer engages TMPRSS2 during the late stages of fusion.

Infrared spectroscopy enables rapid, robust, portable COVID-19 saliva screening based on pathophysiological response to SARS-CoV-2 (preprint)

Fourier-transform infrared (FTIR) spectroscopy provides a (bio)chemical snapshot of the sample, and was recently proposed for COVID-19 saliva screening in proof-of-concept cohort studies. As a step towards translation of this technology, we conducted controlled validation experiments in multiple biological systems. SARS-CoV-2 or UV-inactivated SARS-CoV-2 were used to infect Vero E6 cells in vitro , and K18-hACE2 mice in vivo . Potentially infectious culture supernatant or mouse oral lavage samples were treated with ethanol or Trizol to 75% (v/v) for attenuated total reflectance (ATR)-FTIR spectroscopy, or RT-PCR, respectively. The control condition, UV-inactivated SARS-CoV-2 elicited strong biochemical changes in culture supernatant/oral lavage despite lack of replication determined by RT-PCR or cell culture infectious dose 50%. Crucially, we show that active SARS-CoV-2 infection induced additional FTIR signals over the UV-inactivated SARS-CoV-2 infection, which correspond to innate immune response, aggregated proteins, and RNA. For human patient cohort prediction, we achieved high sensitivity of 93.48% on leave-on-out cross validation (n=104 participants) for predicting COVID-19 positivity using a partial least squares discriminant analysis model, in agreement with recent studies. However, COVID-19 patients negative on follow-up (RT-PCR on day of saliva sampling) were poorly predicted in this model. Importantly, COVID-19 vaccination did not lead to mis-classification of COVID-19 negatives. Meta-analysis revealed SARS-CoV-2 induced increase in Amide II band in all arms of this study and recent studies, indicative of altered β-sheet structures in secreted proteins. In conclusion, ATR-FTIR is a robust, simple, portable method for COVID-19 saliva screening based on detection of pathophysiological responses to SARS-CoV-2.

Epidemiological and Genomic analysis of a Sydney Hospital COVID-19 Outbreak (preprint)

Australia’s early COVID-19 experience involved clusters in northern Sydney, including hospital and aged-care facility (ACF) outbreaks. We explore transmission dynamics, drivers and outcomes of a metropolitan hospital COVID-19 outbreak that occurred in the context of established local community transmission. A retrospective cohort analysis is presented, with integration of viral genome sequencing, clinical and epidemiological data. We demonstrate using genomic epidemiology that the hospital outbreak (n=23) was linked to a concurrent outbreak at a local aged care facility, but was phylogenetically distinct from other community clusters. Thirty day survival was 50% for hospitalised patients (an elderly cohort with significant comorbidities) and 100% for staff. Staff who acquired infection were unable to attend work for a median of 26.5 days (range 14-191); an additional 140 staff were furloughed for quarantine. Transmission from index cases showed a wide dispersion (mean 3.5 persons infected for every patient case and 0.6 persons infected for every staff case). One patient, who received regular nebulised medication prior to their diagnosis being known, acted as an apparent superspreader. No secondary transmissions occurred from isolated cases or contacts who were quarantined prior to becoming infectious. This analysis elaborates the wide-ranging impacts on patients and staff of nosocomial COVID-19 transmission and highlights the utility of genomic analysis as an adjunct to traditional epidemiological investigations. Delayed case recognition resulted in nosocomial transmission but once recognised, prompt action by the outbreak management team and isolation with contact and droplet (without airborne) precautions were sufficient to prevent transmission within this cohort. Our findings support current PPE recommendations in Australia but demonstrate the risk of administering nebulised medications when COVID-19 is circulating locally.