An S1 subunit vaccine and combination adjuvant (COVAC-1) elicits robust protection against SARS-CoV-2 challenge in African green monkeys (preprint)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the agent responsible for the ongoing global pandemic. With over 500 million cases and more than 6 million deaths reported globally, the need for access to effective vaccines is clear. An ideal SARS-CoV-2 vaccine will prevent pathology in the lungs and prevent virus replication in the upper respiratory tract, thus reducing transmission. Here, we assessed the efficacy of an adjuvanted SARS-CoV-2 S1 subunit vaccine, called COVAC-1, in an African green monkey (AGM) model. AGMs immunized and boosted with COVAC-1 were protected from SARS-CoV-2 challenge compared to unvaccinated controls based on reduced pathology and reduced viral RNA levels and infectious virus in the respiratory tract. Both neutralizing antibodies and antibodies capable of mediating antibody-dependent cell-mediated cytotoxicity (ADCC) were observed in vaccinated animals prior to the challenge. COVAC-1 shows effective protection, including in the upper respiratory tract, thus supporting further development and utility for determining the mechanism that confers this protection.

SARS-CoV-2 Omicron variant replication in human respiratory tract ex vivo (preprint)

Emergence of SARS-CoV-2 variants of concern (VOC) with progressively increased transmissibility between humans is a threat to global public health. Omicron variant also evades immunity from natural infection or vaccines 1 . It is unclear whether its exceptional transmissibility is due to immune evasion or inherent virological properties.We compared the replication competence and cellular tropism of the wild type (WT) virus, D614G, Alpha, Beta, Delta and Omicron variants in ex vivo explant cultures of human bronchus and lung. Dependence on TMPRSS2 for infection was also evaluated. We show that Omicron replicated faster than all other SARS-CoV-2 in the bronchus but less efficiently in the lung parenchyma. All VOCs had similar cellular tropism as the WT. Delta was more dependent on serine protease than other VOCs tested.Our findings demonstrate that Omicron is inherently able to replicate faster than other variants known to date and this likely contributes to its inherently higher transmissibility, irrespective of its ability to evade antibody immunity. The lower replication competence of Omicron in human lung may be compatible with reduced severity but the determinants of severe disease are multifactorial. These findings provide important biological clues to the transmissibility and pathogenesis of SARS-CoV-2 VOCs.

Stability of SARS-CoV-2 in different environmental conditions (preprint)

Stability of SARS-CoV-2 in different environmental conditions.