Intranasal vaccine combining adenovirus and trimeric subunit protein provides superior immunity against SARS-CoV-2 Omicron variant

Mucosal immunity provides efficient protection against upper-airway infections, limiting viral shedding and transmission. However, currently, no nasal spray COVID-19 vaccines are approved by WHO for global use. Here we develop a two-component intranasal vaccine that combines an adenovirus vector expressing the spike protein of the XBB.1.5 variant (Ad5XBB.1.5) with a self-assembled trimeric recombinant protein derived from the receptor binding domain (RBDXBB.1.5-HR). This two-component vaccine elicits superior humoral and cellular immunity against XBB.1.5 variants compared with the individual components. It also provides protective immunity against live XBB.1.16 virus challenges in mice, and prevents XBB.1.5 virus transmission in a hamster model. Notably, the activation of the STING signalling pathway in mucosal dendritic cells is essential for the adjuvant effect of the adenovirus vector. We also incorporate another trimeric protein from the BA.5 variant (RBDBA.5-HR), creating a three-component vaccine (Ad5XBB.1.5 + RBDXBB.1.5-HR + RBDBA.5-HR) that shows enhanced broad-spectrum neutralization. The two-component vaccine demonstrates high tolerability and safety in humans, inducing enhanced mucosal immunity and high levels of neutralizing antibodies in all participants. Our findings underscore this strategy for clinical COVID-19 intranasal vaccine development.