Chitosan as an adjuvant for parenterally administered inactivated influenza vaccines

The addition of 0.5% of a chitosan derivative to inactivated influenza vaccines injected parenterally resulted in a four or six to tenfold increase in antibody titres after a single-dose or two-dose intramuscular immunization of mice, respectively, in comparison with antibody titres after immunization without chitosan. Chitosan-adjuvanted vaccines enhanced antibody titers against drift variants of A- and B-type human influenza viruses four to six times compared with the vaccines without chitosan. Inactivated avian influenza virus 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.