Single immunization with MF59-adjuvanted inactivated whole-virion H7N9 influenza vaccine provides early protection against H7N9 virus challenge in mice

Mice were immunized intramuscularly once with different doses of inactivated whole-virion H7N9 influenza vaccine alone or in combination with MF59 adjuvant. Specific IgM and IgG antibody titers in sera of mice were detected by ELISA 3, 5 and 7days after immunization. To evaluate the early protection provided by the vaccine, mice were challenged with lethal dose (40LD50) of homologous virus 3, 5 and 7 days after immunization respectively. The survival rate and body weight change of mice during 21 days after challenge and the residual lung virus titer on 3rd day after challenge were determined. The results demonstrated that mice could obtain effective protection 3 days after immunization with the vaccine at a high dose, and 5-7 days after immunization even at a low dose. Thus early immune responses induced by inactivated whole-virion H7N9 vaccine could provide effective protection.