Vaccination is the most successful and effective medical intervention to prevent infectious diseases, which can reduce mortality, prolong life expectancy and improve quality of life [106]. The development of a vaccine for coronavirus is a critical step in prevention, but it may not be effective for future strains, and we must be ready for the next epidemic [3]. Polysaccharide adjuvant can enhance the immune effect of a vaccine, thus promoting body-specific immunity and non-specific immunity, cellular immunity, humoral immunity and mucosal immunity [107]. Chitosan is effective in stimulating humoral and cell-mediated immune responses with a proven safety record in animals and humans, which has been used as adjuvant for improving vaccine efficacy, especially in RNA virus vaccines [13,108,109]. Chitosan can only modestly protect animals against RSV infection when given post-infection, while it can significantly reduce RSV infection in mice when combined with inactivated RSV vaccine before infection. This study suggested that chitosan can be applied as a potential treatment/adjuvant for RSV infection [13]. Chitosan-adjuvanted vaccines can enhance antibody titers against A- and B-type human influenza viruses 4 to 6 times compared with the vaccines without chitosan. Inactivated AIV A/H5N2 admixed with chitosan, when administered to mice challenged afterwards with the same virus, showed higher immunogenicity and protective efficacy compared with the antigen without chitosan [110]. Chitosan adjuvanted vaccine stored at 4 °C can preserve its adjuvant properties for at least 8 months. Chitosan can stimulate proliferative and cytotoxic activity of splenic mononuclear leukocytes in mice [111]. Thus, chitosan is a promising adjuvant candidate for inactivated influenza vaccines, which provides a reference for the development of anti-novel coronavirus vaccines.