Discussion
Overall, these results suggest that a nasal vaccine containing inactivated WV can be a highly effective means of protection against SARS-CoV-2 infection.
Methods
Mice were immunized subcutaneously (subcutaneous vaccine) or intranasally (nasal vaccine) with the inactivated WV of SARS-CoV-2 as the antigen.
Results
The spike protein (S)-specific IgA level was found to be higher upon nasal vaccination than after subcutaneous vaccination. The level of S-specific IgG in the serum was also increased by the nasal vaccine, although it was lower than that induced by the subcutaneous vaccine. The nasal vaccine exhibited a stronger defense against viral invasion in the upper respiratory tract than the subcutaneous vaccine and unimmunized control; however, both subcutaneous and nasal vaccines provided protection in the lower respiratory tract. Furthermore, we found that intranasally administered inactivated WV elicited robust production of S-specific IgA in the nasal mucosa and IgG in the blood of mice previously vaccinated with messenger RNA encoding the S protein.