# 2320
Twice a year - once for the Northern Hemisphere and once for the Southern Hemisphere - the WHO (World Health Organization) convenes a technical meeting to determine what influenza strains to include in the next flu season's vaccine.
It takes nearly six months of lead time to manufacture enough vaccine for each hemisphere's flu season, and so a decision must be made well in advance.
In the Northern Hemisphere the flu season runs from October through March, and so the selection of flu strains for the next season's vaccine is generally made in February.
Last February it was decided to scrap all of the existing flu strains in this year's northern hemisphere's vaccine, and start over with three newly emerging viruses.
- A/Brisbane/59/2007 (H1N1), replaced A/Solomon Islands/3/2006
- A/Brisbane/10/2007 (H3N2), replaced A/Wisconsin/67/2005
- B/Florida/4/2006, replaced B/Malaysia 2506/2004
It is always a bit of a gamble, deciding six months in advance which flu viruses will be the most prevalent in the next flu season. Usually they get it right, but some years, they miss the mark.
The Southern hemisphere's flu season runs from May through October, and so decisions about 2009's vaccine composition are made in September.
The decision has been made to match the same trivalent formula that the Northern hemisphere will use this fall.
Here is the WHO announcement.
It is recommended that vaccines for use in the 2009 influenza season (southern hemisphere winter) contain the following:
— an A/Brisbane/59/2007 (H1N1)-like virus;*
— an A/Brisbane/10/2007 (H3N2)-like virus;**
— a B/Florida/4/2006-like virus.#
* A/South Dakota/6/2007 (an A/Brisbane/59/2007-like virus) is a current vaccine virus used in live attenuated vaccines.
** A/Brisbane/10/2007 and A/Uruguay/716/2007 (an A/Brisbane/10/2007-like virus) are current vaccine viruses.
# B/Florida/4/2006 and B/Brisbane/3/2007 (a B/Florida/4/2006-like virus) are current vaccine viruses.
For more information
Recommended composition of influenza virus vaccines for use in the 2009 influenza season [pdf 135kb]
A hat tip to Ironorehopper on Flutrackers for posting this link.
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