Combined molnupiravir-nirmatrelvir treatment improves the inhibitory effect on SARS-CoV-2 in macaques.

The periodic emergence of SARS-CoV-2 variants of concern (VOCs) with unpredictable clinical severity and ability to escape preexisting immunity emphasizes the continued need for antiviral interventions. Two small molecule inhibitors, molnupiravir (MK-4482), a nucleoside analog, and nirmatrelvir (PF-07321332), a 3C-like protease inhibitor, have recently been approved as monotherapy for use in high-risk patients with COVID-19. As preclinical data are only available for rodent and ferret models, here we assessed the efficacy of MK-4482 and PF-07321332 alone and in combination against infection with the SARS-CoV-2 Delta VOC in the rhesus macaque COVID-19 model. Macaques were infected with the SARS-CoV-2 Delta variant and treated with vehicle, MK-4482, PF-07321332, or a combination of MK-4482 and PF-07321332. Clinical exams were performed at 1, 2, and 4 days postinfection to assess disease and virological parameters. Notably, use of MK-4482 and PF-07321332 in combination improved the individual inhibitory effect of both drugs, resulting in milder disease progression, stronger reduction of virus shedding from mucosal tissues of the upper respiratory tract, stronger reduction of viral replication in the lower respiratory tract, and reduced lung pathology. Our data strongly indicate superiority of combined MK-4482 and PF-07321332 treatment of SARS-CoV-2 infections as demonstrated in the closest COVID-19 surrogate model of human infection.

Three-Week Old Pigs Are Not Susceptible to Productive Infection with SARS-COV-2.

As the COVID-19 pandemic moves into its third year, there remains a need for additional animal models better recapitulating severe COVID to study SARS-CoV-2 pathogenesis and develop countermeasures, especially treatment options. Pigs are known intermediate hosts for many viruses with zoonotic potential and are susceptible to infection with alpha, beta and delta genera of coronaviruses. Herein, we infected young (3 weeks of age) pigs with SARS-CoV-2 using a combination of respiratory and parenteral inoculation routes. Pigs did not develop clinical disease, nor macroscopic or microscopic pathologic lesions upon SARS-CoV-2 infection. Despite occasional low levels of SARS-CoV-2 genomic RNA in the respiratory tract, subgenomic RNA and infectious virus were never found, and SARS-CoV-2-specific adaptive immune responses were not detectable over the 13-day study period. We concluded that pigs are not susceptible to productive SARS-CoV-2 infection and do not serve as a SARS-CoV-2 reservoir for zoonotic transmission.

UK B.1.1.7 (Alpha) variant exhibits increased respiratory replication and shedding in nonhuman primates.

The continuing emergence of SARS-CoV-2 variants calls for regular assessment to identify differences in viral replication, shedding and associated disease. In this study, we compared African green monkeys infected intranasally with either the UK B.1.1.7 (Alpha) variant or its contemporary D614G progenitor. Both variants caused mild respiratory disease with no significant differences in clinical presentation. Significantly higher levels of viral RNA and infectious virus were found in upper and lower respiratory tract samples and tissues from B.1.1.7 infected animals. Interestingly, D614G infected animals showed significantly higher levels of viral RNA and infectious virus in rectal swabs and gastrointestinal tissues. Our results indicate that B.1.1.7 infection in African green monkeys is associated with increased respiratory replication and shedding but no disease enhancement similar to human B.1.1.7 cases.

A single intranasal dose of chimpanzee adenovirus-vectored vaccine protects against SARS-CoV-2 infection in rhesus macaques.

The deployment of a vaccine that limits transmission and disease likely will be required to end the coronavirus disease 2019 (COVID-19) pandemic. We recently described the protective activity of an intranasally administered chimpanzee adenovirus-vectored vaccine encoding a pre-fusion stabilized spike (S) protein (ChAd-SARS-CoV-2-S [chimpanzee adenovirus-severe acute respiratory syndrome-coronavirus-2-S]) in the upper and lower respiratory tracts of mice expressing the human angiotensin-converting enzyme 2 (ACE2) receptor. Here, we show the immunogenicity and protective efficacy of this vaccine in non-human primates. Rhesus macaques were immunized with ChAd-Control or ChAd-SARS-CoV-2-S and challenged 1 month later by combined intranasal and intrabronchial routes with SARS-CoV-2. A single intranasal dose of ChAd-SARS-CoV-2-S induces neutralizing antibodies and T cell responses and limits or prevents infection in the upper and lower respiratory tracts after SARS-CoV-2 challenge. As ChAd-SARS-CoV-2-S confers protection in non-human primates, it is a promising candidate for limiting SARS-CoV-2 infection and transmission in humans.

Hydroxychloroquine prophylaxis and treatment is ineffective in macaque and hamster SARS-CoV-2 disease models.

We remain largely without effective prophylactic/therapeutic interventions for COVID-19. Although many human COVID-19 clinical trials are ongoing, there remains a deficiency of supportive preclinical drug efficacy studies to help guide decisions. Here we assessed the prophylactic/therapeutic efficacy of hydroxychloroquine (HCQ), a drug of interest for COVID-19 management, in 2 animal disease models. The standard human malaria HCQ prophylaxis (6.5 mg/kg given weekly) and treatment (6.5 mg/kg given daily) did not significantly benefit clinical outcome, nor did it reduce SARS-CoV-2 replication/shedding in the upper and lower respiratory tract in the rhesus macaque disease model. Similarly, when used for prophylaxis or treatment, neither the standard human malaria dose (6.5 mg/kg) nor a high dose (50 mg/kg) of HCQ had any beneficial effect on clinical disease or SARS-CoV-2 kinetics (replication/shedding) in the Syrian hamster disease model. Results from these 2 preclinical animal models may prove helpful in guiding clinical use of HCQ for prophylaxis/treatment of COVID-19.

Respiratory disease in rhesus macaques inoculated with SARS-CoV-2.

An outbreak of coronavirus disease 2019 (COVID-19), which is caused by a novel coronavirus (named SARS-CoV-2) and has a case fatality rate of approximately 2%, started in Wuhan (China) in December 20191,2. Following an unprecedented global spread3, the World Health Organization declared COVID-19 a pandemic on 11 March 2020. Although data on COVID-19 in humans are emerging at a steady pace, some aspects of the pathogenesis of SARS-CoV-2 can be studied in detail only in animal models, in which repeated sampling and tissue collection is possible. Here we show that SARS-CoV-2 causes a respiratory disease in rhesus macaques that lasts between 8 and 16 days. Pulmonary infiltrates, which are a hallmark of COVID-19 in humans, were visible in lung radiographs. We detected high viral loads in swabs from the nose and throat of all of the macaques, as well as in bronchoalveolar lavages; in one macaque, we observed prolonged rectal shedding. Together, the rhesus macaque recapitulates the moderate disease that has been observed in the majority of human cases of COVID-19. The establishment of the rhesus macaque as a model of COVID-19 will increase our understanding of the pathogenesis of this disease, and aid in the development and testing of medical countermeasures.