WHO recommendations for the viruses to be used in the 2012 Southern Hemisphere Influenza Vaccine: Epidemiology, antigenic and genetic characteristics of influenza A(H1N1)pdm09, A(H3N2) and B influenza viruses collected from February to September 2011

► We provide data used for selection of the 2012 southern hemisphere influenza vaccine. ► Influenza activity for the 2011 southern hemisphere season was low or moderate. ► Co-circulation of A(H1N1)pdm09, A(H3N2) and influenza B viruses continued. ► No change was recommended for the 2012 vaccine composition comparing with 2011.