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Twice each year influenza experts gather to discuss recent developments in human and animal influenza viruses around the world, and to decide on the composition of the next influenza season’s flu vaccine.
Due to the time it takes to manufacture a vaccine, decisions on which strains to include must be made six months in advance.
The composition of the northern hemisphere’s vaccine is decided upon in February of each year, and decisions on the southern hemisphere’ vaccine are made in September.
NIAID has a terrific 3-minute video that shows how influenza viruses drift over time, and why the flu shot must be frequently updated, which you can view at this link.
The World Health Organization recently brought together representatives from GISRS (Global Influenza Surveillance and Response System), along with members of OFFLU (the OIE/FAO Network on Animal Influenza), and other experts to determine the composition of next year’s (2014) Southern Hemisphere flu shot.
- The (formerly pandemic) 2009 H1N1 virus continues to circulate and remains surprisingly stable, and so that component remains unchanged.
- Although remaining antigenically similar, H3N2 continues to evolve, and so next year’s formula will see a strain change to an A/Texas/50/2012 (H3N2)-like virus which matches the strain in this fall’s Northern Hemisphere flu shot.
- The influenza B strain selected - a B/Massachusetts/2/2012-like virus (Yamagata lineage) - is the same B strain selected last February for inclusion in this year’s (2013-14) Northern Hemisphere flu vaccine.
- For quadrivalent formulations – available for the first time this year – a second B strain (Victoria Lineage) is recommended; B/Brisbane/60/2008-like virus.
The WHO describes the new recommended H3N2 component as:
`A/Texas/50/2012 is an A(H3N2) virus that following adaptation to growth in eggs has maintained antigenic properties similar to the majority of recently circulating cell - propagated A(H3N2) viruses including A/Victoria/361/2011.’
