Heterotypic immunity to influenza in ferrets

Abstract
Heterotypic immunity to influenza virus in ferrets operated against heterotypic influenza viruses but not heterologous viruses. Contrary to prior reports, the protection conferred lasted for at least 18 mo. This type of immunity limited virus shedding but did not prevent infection. This phenomenon could possibly play a role in determining the severity of infections caused by type A influenza viruses in humans.