Study of immunogenicity and efficacy against Omicron BA.5 of recombinant protein-based COVID-19 vaccine delivered by intramuscular and mucosal routes in nonhuman primates.

BACKGROUND: With SARS-CoV-2 continuing to evolve, there is a need to adapt COVID-19 vaccines to enhance mucosal immunity and better address immune-evasive variants. This pilot study was performed in mice and rhesus macaques to compare Advax-adjuvanted monovalent and bivalent recombinant spike protein vaccines, including when delivered via a combination of intramuscular (IM) and intrapulmonary (IPM) or oral routes. METHODS: Mice were first used to compare the immunogenicity of monovalent and bivalent vaccines containing a variety of spike protein variants. Then, rhesus macaques (n = 23) were divided into 5 groups to receive COVID-19 vaccines via different routes. Clinical signs, local vaccination site reactions, body weight, food consumption, serum, alveolar lavage, nasal and oral antibody levels, and nasal and alveolar lavage virus loads were assessed in response to a heterologous Omicron BA.5 virus challenge. RESULTS: The Wuhan + Mu bivalent vaccine gave the most broadly cross-neutralizing antibody responses. Robust serum neutralizing antibodies against Wuhan, Delta and Lambda variants were obtained, but BA.5 neutralizing antibodies were not detectable pre-challenge. Overall, the IM x3 and the IM x2 plus oral x2 vaccines delivered the best protection, with reduced lung virus load versus unimmunized controls across Days 2, 4 and 7. CONCLUSIONS: Advax-adjuvanted monovalent or bivalent recombinant spike protein vaccines given via parenteral and/or mucosal routes protected against a heterologous BA.5 challenge, despite absent serum BA.5 neutralizing antibody, pre-challenge. The possibility of using an oral Advax-adjuvanted protein booster to provide broad protection against newer SARS-CoV-2 variants warrants further investigation.

In vitro activity of cysteamine against SARS-CoV-2 variants.

Global COVID-19 pandemic is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Continuous emergence of new variants and their rapid spread are jeopardizing vaccine countermeasures to a significant extent. While currently available vaccines are effective at preventing illness associated with SARS-CoV-2 infection, these have been shown to be less effective at preventing breakthrough infection and transmission from a vaccinated individual to others. Here we demonstrate broad antiviral activity of cysteamine HCl in vitro against major emergent infectious variants of SARS-CoV-2 in a highly permissible Vero cell line. Cysteamine HCl inhibited infection of wild type, alpha, beta, gamma, delta, lambda, and omicron variants effectively. Cysteamine is a very well-tolerated US FDA-approved drug used chronically as a topical ophthalmic solution to treat ocular cystinosis in patients who receive it hourly or QID lifelong at concentrations 6 times higher than that required to inhibit SARS CoV-2 in tissue culture. Application of cysteamine as a topical nasal treatment can potentially1) mitigate existing infection 2) prevent infection in exposed individuals, and 3) limit the contagion in vulnerable populations.

Prior infection with SARS-CoV-2 WA1/2020 partially protects rhesus macaques against reinfection with B.1.1.7 and B.1.351 variants.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants that result in increased transmissibility and partial evasion of neutralizing antibodies have recently emerged. Whether natural immunity induced by the original SARS-CoV-2 WA1/2020 strain protects against rechallenge with these SARS-CoV-2 variants remains a critical unresolved question. In this study, we show that natural immunity induced by the WA1/2020 strain leads to partial but incomplete protection against the SARS-CoV-2 variants B.1.1.7 (alpha) and B.1.351 (beta) in rhesus macaques. We challenged rhesus macaques with B.1.1.7 and B.1.351 and showed that infection with these variants resulted in high viral replication in the upper and lower respiratory tract. We then infected rhesus macaques with the WA1/2020 strain and rechallenged them on day 35 with the WA1/2020, B.1.1.7, or B.1.351 variants. Natural immunity to WA1/2020 led to robust protection against rechallenge with WA1/2020 but only partial protection against rechallenge with B.1.351. An intermediate degree of protection was observed in rhesus macaques against rechallenge with B.1.1.7. These data demonstrate partial but incomplete protective efficacy of natural immunity induced by WA1/2020 against SARS-CoV-2 variants of concern. Our findings have important implications for both vaccination and public health strategies in the context of emerging SARS-CoV-2 variants of concern.