Monoglycosylated SARS-CoV-2 receptor binding domain fused with HA-scaffolded protein vaccine confers broad protective immunity against SARS-CoV-2 and influenza viruses.

The SARS-CoV-2 and influenza pandemics have posed a devastating threat to global public health. The best strategy for preventing the further spread of these respiratory viruses worldwide is to administer a vaccine capable of targeting both viruses. Here, we show that a novel monoglycosylated vaccine designed based on the influenza virus HA conserved domain fused with the SARS-CoV-2 spike-RBD domain (HSSR) can present proper antigenicity that elicits sufficient neutralization efficacy against various SARS-CoV-2 variants while simultaneously providing broad protection against H1N1 viruses in mice. Compared with the fully glycosylated HSSR (HSSR), HSSR induced higher ELISA titers targeting HA and spike-RBD and exhibited significantly enhanced neutralization activity against the Wuhan pseudovirus. The enhanced immune responses raised by JR300-adjuvanted HSSR compared to HSSR alone include more anti-HA and anti-spike-RBD antibodies that provide cross-protection against H1N1 challenges and cross-neutralization of SARS-CoV-2 pseudoviruses. Furthermore, the enhanced immune response raised by JR300-adjuvanted-HSSR skews toward a more balanced Th1/Th2 response than that raised by HSSR alone. Notably, HSSR elicited more plasma B cells and memory B cells, and higher IL-4 and IFN-γ cytokine immune responses than spike (S-2P) in mice with preexisting influenza-specific immunity, suggesting that B-cell activation most likely occurs through CD4 T-cell stimulation. This study demonstrated that HSSR produced using a monoglycosylation process and combined with the JR300 adjuvant elicits superior cross-strain immune responses against SARS-CoV-2 and influenza viruses in mice compared with S-2P. JR300-adjuvanted HSSR has great potential as a coronavirus-influenza vaccine that provides dual protection against SARS-CoV-2 and influenza infections.