What strains does the seasonal flu vaccine protect against?

Each flu season, all vaccines are prepared to the latest WHO specifications; WHO recommends that vaccines for use in the 2011-2012 influenza season (northern hemisphere winter) contain the following:

• A/California/7/2009 (H1N1)-like virus, 

• A/Perth/16/2009 (H3N2)-like virus 

• B/Brisbane/60/2008-like virus.

All of this year's vaccines will protect against these strains.

WHO recommends that vaccines for use in the 2012-2013 influenza season (southern hemisphere winter) contain the following:

• an A/California/7/2009 (H1N1)pdm09-like virus;
• an A/Victoria/361/2011 (H3N2)-like virus;
• a B/Wisconsin/1/2010-like virus

You can see more about current flu vaccination strains here.