Intranasal delivery of a rationally attenuated SARS-CoV-2 is immunogenic and protective in Syrian hamsters.

Few live attenuated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines are in pre-clinical or clinical development. We seek to attenuate SARS-CoV-2 (isolate WA1/2020) by removing the polybasic insert within the spike protein and the open reading frames (ORFs) 6-8, and by introducing mutations that abolish non-structural protein 1 (Nsp1)-mediated toxicity. The derived virus (WA1-ΔPRRA-ΔORF6-8-Nsp1K164A/H165A) replicates to 100- to 1000-fold-lower titers than the ancestral virus and induces little lung pathology in both K18-human ACE2 (hACE2) transgenic mice and Syrian hamsters. Immunofluorescence and transcriptomic analyses of infected hamsters confirm that three-pronged genetic modifications attenuate the proinflammatory pathways more than the removal of the polybasic cleavage site alone. Finally, intranasal administration of just 100 PFU of the WA1-ΔPRRA-ΔORF6-8-Nsp1K164A/H165A elicits robust antibody responses in Syrian hamsters and protects against SARS-CoV-2-induced weight loss and pneumonia. As a proof-of-concept study, we demonstrate that live but sufficiently attenuated SARS-CoV-2 vaccines may be attainable by rational design.

In-line miniature 3D-printed pressure-cycled ventilator maintains respiratory homeostasis in swine with induced acute pulmonary injury.

The COVID-19 pandemic demonstrated the need for inexpensive, easy-to-use, rapidly mass-produced resuscitation devices that could be quickly distributed in areas of critical need. In-line miniature ventilators based on principles of fluidics ventilate patients by automatically oscillating between forced inspiration and assisted expiration as airway pressure changes, requiring only a continuous supply of pressurized oxygen. Here, we designed three miniature ventilator models to operate in specific pressure ranges along a continuum of clinical lung injury (mild, moderate, and severe injury). Three-dimensional (3D)-printed prototype devices evaluated in a lung simulator generated airway pressures, tidal volumes, and minute ventilation within the targeted range for the state of lung disease each was designed to support. In testing in domestic swine before and after induction of pulmonary injury, the ventilators for mild and moderate injury met the design criteria when matched with the appropriate degree of lung injury. Although the ventilator for severe injury provided the specified design pressures, respiratory rate was elevated with reduced minute ventilation, a result of lung compliance below design parameters. Respiratory rate reflected how well each ventilator matched the injury state of the lungs and could guide selection of ventilator models in clinical use. This simple device could help mitigate shortages of conventional ventilators during pandemics and other disasters requiring rapid access to advanced airway management, or in transport applications for hands-free ventilation.

Long-term immunity in convalescent Syrian hamsters provides protection against new-variant SARS-CoV-2 infection of the lower but not upper respiratory tract.

COVID-19 vaccines provide high levels of protection against severe disease and hospitalization due to severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) infection. Vaccination may be less effective in preventing shedding of infectious viruses from otherwise immune patients. In this study, we describe breakthrough infections and shedding of infectious viruses in convalescent hamsters without significant replication in the lower respiratory tract following reinfection by Alpha and Delta variants despite high levels of circulating antibodies in sera. Using convalescent hamsters with long-term immunity (up to 1 year) following infection by ancestral SARS-CoV-2, we can model aspects of recurring COVID-19 in the context of preexisting immunity.

SARS-CoV-2 infection induces protective immunity and limits transmission in Syrian hamsters.

A critical question in understanding the immunity to SARS-COV-2 is whether recovered patients are protected against re-challenge and transmission upon second exposure. We developed a Syrian hamster model in which intranasal inoculation of just 100 TCID50 virus caused viral pneumonia. Aged hamsters developed more severe disease and even succumbed to SARS-CoV-2 infection, representing the first lethal model using genetically unmodified laboratory animals. After initial viral clearance, the hamsters were re-challenged with 105 TCID50 SARS-CoV-2 and displayed more than 4 log reduction in median viral loads in both nasal washes and lungs in comparison to primary infections. Most importantly, re-challenged hamsters were unable to transmit virus to naïve hamsters, and this was accompanied by the presence of neutralizing antibodies. Altogether, these results show that SARS-CoV-2 infection induces protective immunity that not only prevents re-exposure but also limits transmission in hamsters. These findings may help guide public health policies and vaccine development and aid evaluation of effective vaccines against SARS-CoV-2.

SARS-CoV-2 B.1.1.7 Infection of Syrian Hamster Does Not Cause More Severe Disease, and Naturally Acquired Immunity Confers Protection.

Epidemiological studies have revealed the emergence of multiple severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VOC), including the lineage B.1.1.7 that is rapidly replacing old variants. The B.1.1.7 variant has been linked to increased morbidity rates, transmissibility, and potentially mortality. To assess viral fitness in vivo and to address whether the B.1.1.7 variant is capable of immune escape, we conducted infection and reinfection studies in naive and convalescent Syrian hamsters (>10 months old). Nasal wash samples from hamsters infected by a B.1.1.7 variant exhibited slightly higher viral RNA levels but lower infectious titers than those from B.1 (G614) variant-infected hamsters, and the two variants induced comparable lung pathologies in hamsters. Despite a sporadic and transient low-level infection in the nasal cavity, convalescent hamsters that had recovered from a previous USA-WA1 isolate (D614) infection displayed no observable clinical signs or lung pathology following B.1.1.7 rechallenge. Altogether, our study did not find that the B.1.1.7 variant significantly differs from the B.1 variant in pathogenicity in Syrian hamsters and that a heterologous natural infection-induced immunity confers protection against a secondary challenge by the B1.1.7 variant. IMPORTANCE The rapid emergence of several variants of concern of SARS-CoV-2 calls for evaluations of viral fitness and pathogenicity in animal models in order to understand the mechanism of enhanced transmission and the possible increases in morbidity and mortality rates. Here, we demonstrated that immunity naturally acquired through a prior infection with the first-wave variant does confer nearly complete protection against the B.1.1.7 variant in Syrian hamsters upon reexposure. Strikingly, although the B.1.1.7 variant appears to replicate to a higher level in the nose than the ancestral B.1 variant, it does not induce more severe lung pathology in hamsters.