In vitro characterisation of SARS-CoV-2 and susceptibility of domestic ferrets (Mustela putorius furo).

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is an emerging virus that has caused significant human morbidity and mortality since its detection in late 2019. With the rapid emergence has come an unprecedented programme of vaccine development with at least 300 candidates under development. Ferrets have proven to be an appropriate animal model for testing safety and efficacy of SARS-CoV-2 vaccines due to quantifiable virus shedding in nasal washes and oral swabs. Here, we outline our efforts early in the SARS-CoV-2 outbreak to propagate and characterize an Australian isolate of the virus in vitro and in an ex vivo model of human airway epithelium, as well as to demonstrate the susceptibility of domestic ferrets (Mustela putorius furo) to SARS-CoV-2 infection following intranasal challenge.

Type I Hypersensitivity in Ferrets Following Exposure to SARS-CoV-2 Inoculum: Lessons Learned.

This case report discusses Type I hypersensitivity in ferrets following exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) inoculum, observed during a study investigating the efficacy of candidate COVID-19 vaccines. Following a comprehensive internal root-cause investigation, it was hypothesized that prior prime-boost immunization of ferrets with a commercial canine C3 vaccine to protect against the canine distemper virus had resulted in primary immune response to fetal bovine serum (FBS) in the C3 preparation. Upon intranasal exposure to SARS-CoV-2 virus cultured in medium containing FBS, an allergic airway response occurred in 6 out of 56 of the ferrets. The 6 impacted ferrets were randomly dispersed across study groups, including different COVID-19 vaccine candidates, routes of vaccine candidate administration, and controls (placebo). The root-cause investigation and subsequent analysis determined that the allergic reaction was unrelated to the COVID-19 vaccine candidates under evaluation. Histological assessment suggested that the allergic response was characterized by eosinophilic airway disease; increased serum immunoglobulin levels reactive to FBS further suggested this response was caused by immune priming to FBS present in the C3 vaccine. This was further supported by in vivo studies demonstrating ferrets administered diluted FBS also presented clinical signs consistent with a hyperallergic response, while clinical signs were absent in ferrets that received a serum-free SARS-CoV-2 inoculum. It is therefore recommended that vaccine studies in higher order animals should consider the impact of welfare vaccination and use serum-free inoculum whenever possible.

Experimental and in silico evidence suggests vaccines are unlikely to be affected by D614G mutation in SARS-CoV-2 spike protein.

The 'D614G' mutation (Aspartate-to-Glycine change at position 614) of the SARS-CoV-2 spike protein has been speculated to adversely affect the efficacy of most vaccines and countermeasures that target this glycoprotein, necessitating frequent vaccine matching. Virus neutralisation assays were performed using sera from ferrets which received two doses of the INO-4800 COVID-19 vaccine, and Australian virus isolates (VIC01, SA01 and VIC31) which either possess or lack this mutation but are otherwise comparable. Through this approach, supported by biomolecular modelling of this mutation and the commonly-associated P314L mutation in the RNA-dependent RNA polymerase, we have shown that there is no experimental evidence to support this speculation. We additionally demonstrate that the putative elastase cleavage site introduced by the D614G mutation is unlikely to be accessible to proteases.