Resurgence of Pandemic A/H1N1 2009 Viruses during Influenza Season 2013-2014

In April 2009, the world has known an emergence of a triple-reasserting influenza virus, pandemic A/H1N1, causing a pandemic around the world. The virus has continued to circulate during influenza seasons from 2010 to 2013, but with low frequencies. However, during the influenza season 2013-2014, we have assisted to the resurgence of this same virus worldwide. A comparison of the 2009-2010 and the 2013-2014 influenza seasons revealed a notable change regarding the epidemiology of this virus, in term of hospitalizations and deaths associated with pandemic A/H1N1: A gradual transition of hospitalizations and deaths for older ages related to influenza has been reported.
The resurgence of pandemic A/H1N1 is critical and its explanation is still difficult, but could be related to the viral genetic and/or the host susceptibility. Therefore, the best management of the disease and the effective control of the virus can be attempted by vaccination of all persons without contraindications and strengthening the surveillance systems of influenza.