Yesterday the CDC released an alert that described an unfortunate phenomenon that has occurred with this year's flu season: a vaccine mismatch. This is not a surprising development as mismatches are known to happen as predicting flu strains can be very difficult given flu's ability to shift and drift. But when such mismatches occur they can be expected to diminish the 60% effectiveness of the vaccine.
What happened this year was that the H3N2 strain included in the vaccine does not match over half of the H3N2 strains isolated thus far. If H3N2 strains were only predicted to be a minor part of this year's flu season this fact might not much a difference, but it looks like we might be in for an H3N2 dominant season so this could become very significant. In general, H3N2 seasons tend to be more severe than those dominated by other strains so we may be in for a rough winter.
The mismatched strain, which first appeared in March 2014, has already been slated for inclusion in the upcoming vaccine for the Southern Hemisphere, whose flu season is the mirror image of the Northern Hemisphere's season. But, given the lead time needed to make flu vaccines, it's not something that could have been incorporated into this season's Northern Hemisphere vaccine.
It's important to remember that, despite the mismatch, the flu vaccine is something that everyone should still received as this mismatch is only for 1 of 4 strains and the other strains will certainly cause disease this season.
The only way to eliminate the chances of future mismatches is the development of a universal flu vaccine that targets a part of the virus that does not change. That would be a true game changer.