Virological surveillance of the influenza A(H1N1)2009 pandemic: the role of the belgian national influenza centre

On 24 April 2009, the World Health Organization (WHO) first reported the emergence of a new Influenza virus in the United States of America and Mexico [ 1 ]. This novel Influenza virus was identified as a new subtype A(H1N1) resulting from a reassortment of avian, human and swine Influenza viruses. This virus, which was later on referred to as A(H1N1)2009, rapidly demonstrated its capacity to transmit among humans [ 2 ]. On 11 June 2009, the WHO decided to raise the pandemic alert phase to its maximum level (phase 6) [ 3 ].