Credit NIAID
# 10,561
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 and distribute a vaccine, decisions on which strains to include must be made six months in advance.
Which means the composition of the northern hemisphere’s vaccine must be decided upon in February of each year, while 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.
Note: This fall’s 2015-16 Northern Hemisphere vaccine is identical to the vaccine just used in the Southern Hemisphere. It contains:
- an A/California/7/2009 (H1N1)pdm09-like virus;
- an A/Switzerland/9715293/2013 (H3N2)-like virus;
- a B/Phuket/3073/2013-like virus.
It is recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Brisbane/60/2008-like virus.
Times, and flu viruses, change . . . and so must the formulation for next year’s Southern Hemisphere flu shot. You’ll note two changes – a slightly different H3N2 strain has been selected, and a switch from the B/Yamagata strain which has been used for the past couple of years, back to a B/Victoria strain.
24 September 2015
It is recommended that trivalent vaccines for use in the 2016 influenza season (southern hemisphere winter) contain the following:
- an A/California/7/2009 (H1N1)pdm09-like virus;
- an A/Hong Kong/4801/2014 (H3N2)-like virus;
- a B/Brisbane/60/2008-like virus.
It is recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Phuket/3073/2013-like virus.
The switch back to a B/Victoria strain was telegraphed early last month when in Eurosurveillance: B/Victoria Prevalence In Early New South Wales Flu Season we saw early reports of a shift in Influenza B dominance, away from the Yamagata lineage in Australia.
And it is the reason why, as I wrote earlier this month in #NatlPrep: Giving Preparedness A Shot In The Arm, I decided to go with the quadrivalent vaccine this year, as it contains both B lineages.
Of course, there is always the danger that during the manufacturing or service period for this vaccine a new flu virus could emerge (as happened with pH1N1 in 2009), or that one of the currently circulating viruses changes enough antigenically to evade the vaccine (as happened last year with H3N2).
A year is a long time to prognosticate the future of influenza.
Yet despite these challenges, most years the flu vaccine turns out to provide at least a moderate level of protection (see CDC Vaccine Effectiveness - How Well Does the Flu Vaccine Work?), and along with good flu hygiene (washing hands, covering coughs, etc.), are your best protection against catching the flu.
