Single intranasal immunization with a high dose of influenza vector protects against infection with heterologous influenza virus and SARS-CoV-2 in ferrets and hamsters

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BACKGROUND: The challenge of vaccine effectiveness against viruses that undergo constant antigenic changes during evolution is currently being addressed by updating vaccine formulations to match circulating strains. However, this approach proves ineffective if a virus undergoes antigenic drift and shift, or if a new virus, such as SARS-CoV-2, emerges and enters circulation. Hence, there is a pressing need to develop universal vaccines that elicit a T-cell immune response targeting conserved antigenic determinants of pathogens. OBJECTIVE: To develop a vaccine candidate against influenza virus and coronavirus based on an attenuated influenza vector. METHODS: In pursuit of this objective, we developed a recombinant influenza vector named FluCoV-N. It incorporates attenuating modifications in the ns1 and nep genes and expresses the N-terminal half of the N protein (N1-209) of the SARS-CoV-2 virus. To assess the vector’s protective efficacy against influenza, ferrets were infected with heterologous influenza A/Austria/1516645/2022 (H3N2) virus on the 25th day after a single immunization with 9.4 log10EID50 of the studied vector. To test protection against coronavirus, hamsters were immunized once with the vector at a dose of 8.2 log10EID50 and challenged with SARS-CoV-2 virus 21 days later. RESULTS: As a result of modifications to the NS genomic segment, the constructed vector acquired a temperature-sensitive (ts) phenotype and demonstrated a heightened ability to induce type 1 interferons. It was harmless to animals when administered intranasally at high doses exceeding 8.0 log10EID50. In ferrets, a single intranasal immunization with FluCoV-N accelerated the resolution of infection caused by heterologous influenza H3N2 virus. Similar immunization in hamsters led to a 10,000-fold reduction in SARS-CoV-2 viral titers in the lungs on the second day after challenge and reduced pathology in the lungs of animals. CONCLUSION: A single intranasal immunization with the FluCoV-N vector protected from heterologous influenza or SARS-CoV-2 viruses in ferrets and hamsters.