The Development of Live-Attenuated Vaccines for Pandemic Influenza

The emergence of highly pathogenic H5N1 avian influenza A viruses in humans since 1997 has raised concerns that we may be facing the next influenza pandemic. Since 2003, there have been over 400 confirmed cases of human infection with highly pathogenic H5N1 avian influenza in 15 countries worldwide, with a case fatality rate of 63% (http://www.who.int.csr/disease/avian_influenza/country/cases_table_2008_12_09/en/index.html, accessed March 6 2009). In addition, since 1999, sporadic human infections with avian influenza viruses of the H7, H9 and H10 subtypes have occurred, resulting in disease of varying severity, from mild upper-respiratory infection to severe pneumonia and death [1–8]. Although the majority of avian influenza (AI) infections in humans have been caused by H5N1 AI viruses, the next pandemic could be caused by an influenza A virus of any of the 16 hemagglutinin (HA) subtypes known to infect birds. Influenza A viruses also infect a wide variety of mammalian species in nature, presenting another source from which humans could acquire infection. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.