Comparison of adjuvant efficacy of chitosan and aluminum hydroxide for intraperitoneally administered inactivated influenza H5N1 vaccine.

A safe and effective adjuvant is important to develop vaccines against highly pathogenic avian influenza virus. Chitosan, a derivative from the natural amino polysaccharide chitin, has been proved to be an effective adjuvant for inactivated influenza virus vaccine. In this study, protective immunity in mice provided by chitosan-adjuvanted inactivated H5N1 vaccine was compared with that from an aluminum hydroxide-adjuvanted one. Mice were injected intraperitoneally once or twice with various dosages of inactivated vaccine alone or in combination with an adjuvant (chitosan or aluminum hydroxide). To test the immunization effect, mice were challenged with a lethal dose of H5N1 virus. The results showed that the adjuvanted vaccines were more effective than adjuvant-free ones in inducing humoral immune responses and protecting mice against lethal challenge. Chitosan was comparable to the alum adjuvant in efficacy. These findings indicated that chitosan might be a candidate adjuvant for parenteral administration of inactivated influenza vaccines.