Every year, the number of cases of influenza rises during the winter seasons in the northern and southern hemispheres.

 

The type and composition of influenza viruses circulating in countries change from season to season. Through the Global Influenza Surveillance Network, WHO continually gathers information on the strains currently in circulation. Based on these findings and in consultation with experts, WHO makes recommendations to national public health authorities and vaccine manufacturers on the composition of influenza vaccines for the next winter season: that is, on which viruses should be included/considered for vaccination.

WHO has issued recommendations for the composition of virus vaccines for the southern hemisphere winter season in 2010. They include producing vaccines based on three viruses: an A/Perth/16/2009 (H3N2)-like virus, a B/Brisbane /60/2008-like virus and an A/California/7/2009 (H1N1)-like virus (covering the pandemic (H1N1) 2009 virus). Recommendations on the presentation of the vaccines – whether the viruses should be contained in a single vaccine or in one for pandemic (H1N1) 2009 influenza and another for seasonal influenza – will be provided later.

The seasonal A(H1N1) influenza virus is not one of those that WHO recommends including in the vaccine composition. In addition, the A(H3N2) virus included in the recommendation is different to the A(H3N2) strain that is included in the vaccine for seasonal influenza in the northern hemisphere for winter 2009.

WHO/Europe, in collaboration with Member States, will therefore continue carefully to monitor the circulation and prevalence of both seasonal and pandemic influenza virus strains, to determine early any potential vaccine mismatch and to inform treatment strategies for risk groups. In addition, this information will contribute to the recommendations to be made in spring 2010 for the composition of the 2010 northern hemisphere influenza vaccine.