WHO recommends that the following viruses be used for influenza vaccines in the 2010-2011 influenza season in the northern hemisphere:
• an A/California/7/2009 (H1N1)-like virus (pandemic H1N1 2009 virus; pH1N1)
• an A/Perth/16/2009 (H3N2)-like virus
• a B/Brisbane/60/2008-like virus.
Recommendations are based on epidemiological, genetic and serological tests on influenza virus isolates collected through the WHO Global Influenza Surveillance Network between September 2009 and January 2010.
On August 10, 2010, WHO announced that the world has moved into the post-pandemic period.
During the post-pandemic period, pH1N1 appears to be taking on the behaviour of a seasonal virus and co-circulating with other seasonal influenza strains. However, pH1N1 will likely continue to affect younger age groups disproportionately as seen during the 2009 pandemic.
Current influenza activity in temperate countries in the southern hemisphere (Argentina, Chile, New Zealand, Australia, and South Africa) provides us with information on possible influenza scenarios during the winter months in the northern hemisphere. Whereas seasonal influenza A/H1N1 viruses are undetectable in all five countries, influenza pH1N1, A/H3N2 and B viruses have been reported and their proportions in circulation in each country have been variable.
The recommended trivalent seasonal vaccine for the northern hemisphere 2010-2011 season will provide protection against influenza pH1N1, A/H3N2 and B viruses.