Protection of ferrets from infection by swine-origin 2009 A (H1N1) influenza virus by the inactivated vaccine.

Swine-origin pandemic 2009 A (H1N1) influenza viruses are still infecting humans, and humans are currently being vaccinated with the inactivated vaccine of 2009 A (H1N1) influenza virus. We wanted to determine the efficacy of 2009 A (H1N1) inactivated vaccine in ferrets. Ferrets immunized with one dose (7.5 microg) of 2009 A (H1N1) inactivated vaccine were not protected from infections of either pandemic H1N1 or seasonal H1N1 influenza viruses, while ferrets immunized with two doses of 2009 A (H1N1) inactivated vaccine were protected from infections of pandemic H1N1, but not seasonal H1N1 influenza viruses. IgG subtype of antibody was dominantly detected in tissues of immunized ferrets. Our study suggests that pandemic H1N1 vaccine may not elicit the antibody cross-reactive to the seasonal H1N1 influenza virus.