Influenza A(H1N1) 2009 virus: current situation and post-pandemic recommendations

Since its emergence in April 2009, pandemic influenza A(H1N1) 2009 virus has affected all parts of the world, causing the first influenza pandemic since 1968. Following the observation that 1 or 2 epidemic periods had occurred in most countries and in most WHO Regions, WHO declared on 10 August 2010 that the world was moving into the post-pandemic period. Based on experiences with past pandemics, the pandemic influenza A(H1N1) 2009 virus was expected to take on the behaviour of a seasonal influenza virus and continue to circulate. However, localized outbreaks or epidemics that include serious disease in younger age groups were expected to continue during the immediate post-pandemic period. At the time of WHO's announcement, India, New Zealand and several countries in the Caribbean were experiencing widespread, and in some places intense, transmission of the pandemic influenza A(H1N1) 2009, while other countries were reporting active circulation of seasonal influenza A(H3N2) and type-B viruses.