Beta Spike-Presenting SARS-CoV-2 Virus-Like Particle Vaccine Confers Broad Protection against Other VOCs in Mice

Vaccine antigens must present the correct conformation of viral fusion glycoproteins to elicit effective immune responses. Virus-like particles (VLPs) serve as promising vaccine platforms because they mimic the membrane-embedded conformations of fusion glycoproteins on native viruses. Here, we employed SARS-CoV-2 VLPs (SMEN) presenting ancestral, Beta, or Omicron spikes to identify the variant that elicits potent and cross-protective immune responses in the highly sensitive K18-hACE2 mouse model. A combined intranasal and intramuscular administration regimen of the SMEN vaccine generated effective immune responses and was predominantly mediated by antibodies with minor contributions from T cells. Immunization with SMEN presenting an ancestral spike resulted in 100, 75, or 0% protection against ancestral, Delta or Beta VOC-induced mortality, respectively, whereas SMEN presenting the most divergent Omicron spike provided only limited protection (50%, 0%, and 25%) against ancestral, Delta, and Beta variants, respectively. By contrast, SMEN with a Beta spike offered 100% protection against the variants used in this study. Thus, the Beta variant not only overcame the immunity produced by other variants, but also elicited diverse and effective immune response. Our findings suggest that leveraging the Beta variant spike protein can enhance SARS-CoV-2 immunity, potentially leading to a more comprehensive vaccine against emerging variants.