Publication date: Jul 19, 2025

The emergence of divergent SARS-CoV-2 variants has significantly compromised the effectiveness of first-generation COVID-19 vaccines. We investigated a prime-boost approach using bovine adenoviral (Ad) [BAd] and human Ad (HAd) vectors expressing the spike (S), membrane (M), or nucleocapsid (N) with the autophagy-inducing peptide C5 (AIP-C5) for enhanced antigen-specific immunity. The combinational vaccine formulation expressing three antigens demonstrated markedly elevated antigen-specific cell-mediated immune (CMI) responses compared to groups immunized with vectors expressing individual antigens. Furthermore, vaccinated animals exhibited 100% survival, significant reductions in lung viral titers, and no apparent signs of morbidity following challenges with Delta or Omicron variants in K18-hACE2 transgenic mice. Surprisingly, immunization with vectors expressing M and N resulted in immune suppression. However, including S with M and N overcomes this antagonistic interaction and significantly enhances immune responses and protection efficacy. Using the BAd vaccine platform in a multi-antigen approach complemented with AIP-C5 is a promising strategy for developing next-generation SARS-CoV-2 vaccines.

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