# 5753
It takes roughly six months to develop, manufacture, and ship large quantities of the yearly flu vaccine – and that means that decisions on which three influenza strains to include in the flu shot must be made a full half-year before the upcoming flu season.
The rub is, flu strains are constantly changing and it is possible for new, antigenically different strains to appear in the interim.
And that’s exactly what happened when the H1N1 swine flu appeared in late April of 2009.
Luckily that was early enough in the year to allow time to produce an emergency pandemic vaccine for the fall.
Although this fall’s flu vaccine is already shipping, scientists around the world will continue to examine flu samples looking signs of trouble; indications that one or more of the viruses in circulation have evolved or `drifted’ away from the vaccine.
While we talk about four main strains of influenza that circulate in humans (A/H1N1(pdm), A/H3N2, B Victoria, B Yamagata) – in reality there is a good deal more diversity in flu strains than that.
When a strain is said to be `antigenically similar’ to the vaccine strain, it is expected (but not assured) that the vaccine remains reasonably effective.
The latest analysis of flu samples out of Europe was released yesterday by the ECDC - and as one would expect - we continue to see viral evolution in action and increasing diversity among the strains in circulation.
The good news is that while they continue to evolve, most (but not all) of these isolates appear to remain antigenically similar to this year’s vaccine.
Influenza virus characterisation, summary Europe, July 2011
Surveillance reports - 12 Aug 2011
ABSTRACT
Influenza A(H1N1)pdm, influenza A(H3N2), and influenza B/Victoria- and B/Yamagata-lineage viruses have been characterised genetically and antigenically.
- Recently isolated A(H1N1)pdm viruses continue to fall into several genetic groups but all groups show antigenic similarity to the currently recommended vaccine virus A/California/7/2009.
- A(H3N2) viruses fall into distinct genetic groups but there is no consistent correlation of altered antigenicity with any genetic group, compared with the vaccine virus A/Perth/16/2009.
- Influenza B viruses of the B/Victoria/2/87 lineage predominate over those of the B/Yamagata/16/88 lineage. Most of the B/Victoria/2/87 lineage viruses remain genetically and antigenically similar to the currently recommended vaccine virus B/Brisbane/60/2008.
- The majority of influenza B viruses of the B/Yamagata-lineage are in the B/Bangladesh/3333/2007 genetic clade
but viruses received from three countries with Baltic coastlines fall within a different genetic clade.
It’s always a bit of a crap shoot when scientists have to pick just 3 influenza strains - 6 months in advance - to put in the seasonal vaccine.
While it isn’t possible to cover all of the viral bases with a trivalent (3 strain) vaccine - this year’s vaccine still looks to be a pretty good match for the bulk of the flu viruses now in circulation.
How good?
Well, we won’t know that until this year’s flu season has run its course.
While getting a flu shot won’t guarantee that you won’t catch the flu (and doesn’t protect against other flu-like illnesses), the CDC considers the yearly flu shot to be the best way to protect yourself, your family, and your community during the upcoming flu season.
This from the CDC’s Q&A About The 2011-2012 Flu Season:
What should I do to prepare for this flu season?
CDC recommends a yearly flu vaccine for everyone 6 months of age and older as the first and most important step in protecting against this serious disease. While there are many different flu viruses, the flu vaccine is designed to protect against the three main flu strains that research indicates will cause the most illness during the flu season.
For information about which viruses this season's vaccine will protect against visit Vaccine Selection for the 2011–2012 Season. Getting the flu vaccine as soon as it becomes available each year is always a good idea, and the protection you get from vaccination will last throughout the flu season.
For more on the upcoming flu season, visit the CDC’s Flu.gov website.
