Intranasal Inactivated Sarbecovirus Vaccine With TLR7/8 Agonist Adjuvant Elicits Cross-Reactive Mucosal and Systemic Immunity Against SARS-CoV-2 Variants and Pre-Emergent Bat Coronaviruses

This study investigates intranasal inactivated pan-sarbecovirus vaccine adjuvanted with TLR7/8 agonist inducing cross-reactive mucosal IgA, neutralizing antibodies, and T cell responses against SARS-CoV-2 variants and bat sarbecoviruses in macaque and hamster models within the context of vaccine immunology and pandemic preparedness, an area of growing scientific importance given its implications for pan-sarbecovirus pandemic preparedness vaccine development, mucosal COVID booster strategy, and TLR7/8 adjuvant intranasal formulation platform. Using intranasal prime-boost immunization (day 0 and 28) in 8 rhesus macaques and 24 Syrian hamsters per group; nasal IgA, serum IgG, pseudovirus neutralization (pVNT50), T cell ELIspot; challenge with 1e5 TCID50 WA1, BA.4/5, XBB.1.5, or WIV1 at day 56, we examine intranasal delivery targeting nasal-associated lymphoid tissue (NALT) inducing secretory IgA at respiratory mucosa — the primary site of SARS-CoV-2 entry — which intramuscular vaccination fails to elicit; TLR7/8 agonist adjuvant activating innate pDC and cDC1 for strong Th1 polarization and memory B cell priming in Macaque study: 8/arm x 5 arms (WA1 intranasal, WA1 intramuscular, adjuvant only, WIV1 intranasal, saline control) = 40 macaques; Hamster challenge: 24/arm x 4 challenge strains = 96 hamsters drawn from Pacific Virology Institute BSL-3 facility for macaque and hamster challenge studies; ABSL-3 for bat coronavirus WIV1 challenge; pVNT50 in BSL-2 with lentiviral pseudoviruses expressing sarbecovirus spike proteins. Results indicate that intranasal vaccine elicits nasal IgA titer 284-fold higher than intramuscular (p<0.001); pVNT50 against BA.4/5 1:484, XBB.1.5 1:248, WIV1 1:84; nasal viral load at day 3 reduced 3.84-log10 vs. saline (p<0.001); lung pathology score 0.84 vs. 3.84 (saline, p<0.001) (p < 0.001), with nasal IgA 284x vs. IM; pVNT50 WIV1 1:84; 3.84-log viral load reduction; lung score 0.84 vs. 3.84 as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to vaccine immunology and pandemic preparedness and carry actionable implications for the design of programs and policies targeting pan-sarbecovirus pandemic preparedness vaccine development, mucosal COVID booster strategy, and TLR7/8 adjuvant intranasal formulation platform.