Multidrug-resistant 2009 pandemic influenza A(H1N1) viruses maintain fitness and transmissibility in ferrets.

Background: The 2009 influenza A(H1N1) pandemic called attention to the limited influenza treatment options available, especially in individuals at high risk of severe disease. Neuraminidase inhibitor-resistant seasonal H1N1 viruses have demonstrated the ability to transmit well despite early data indicating that resistance reduces viral fitness. 2009 H1N1 pandemic viruses have sporadically appeared containing resistance to neuraminidase inhibitors and the adamantanes, but the ability of these viruses to replicate, transmit, and cause disease in mammalian hosts has not been fully characterized.

The PB2-E627K mutation attenuates viruses containing the 2009 H1N1 influenza pandemic polymerase.

The swine-origin H1N1 influenza A virus emerged in early 2009 and caused the first influenza pandemic in 41 years. The virus has spread efficiently to both the Northern and the Southern Hemispheres and has been associated with over 16,000 deaths. Given the virus's recent zoonotic origin, there is concern that the virus could acquire signature mutations associated with the enhanced pathogenicity of previous pandemic viruses or H5N1 viruses with pandemic potential.

Prior infection with classical swine H1N1 influenza viruses is associated with protective immunity to the 2009 pandemic H1N1 virus.

Background: The 2009 H1N1 pandemic emerged even though seasonal H1N1 viruses have circulated for decades. Epidemiological evidence suggested that the current seasonal vaccine did not offer significant protection from the novel pandemic, and that people over the age of 50 were less susceptible to infection.

Objectives: In a mouse challenge study with the 2009 pandemic H1N1 virus, we evaluated protective immune responses elicited by prior infection with human and swine influenza A viruses.

Rapid selection of a transmissible multidrug-resistant influenza A/H3N2 virus in an immunocompromised host.

Background: The overall impact of influenza virus infection in immunocompromised patients is largely unknown. Antigenic drift and genetic variations during prolonged influenza infection have been demonstrated. In this report we describe a multidrug-resistant H3N2 influenza virus isolated from an immunocompromised patient after 5 days of therapy.

Rapid selection of oseltamivir- and peramivir-resistant pandemic H1N1 virus during therapy in 2 immunocompromised hosts.

Pandemic 2009 H1N1 virus isolates containing the neuraminidase inhibitor resistance mutation H275Y have been reported. We describe rapid selection for the H275Y resistance mutation during therapy in 2 immunocompromised individuals at 9 and 14 days of therapy, as well as the first described case of clinically significant resistance to peramivir.