That's even more crucial right now, because the CDC is starting to see a shift in which strains are circulating among Americans. Thus far, H3N2 has been the predominant virus type, which is why we've seen so many hospitalizations. H3N2 seems to be more dangerous in general, particularly for folks in the Baby Boomer generation (more on that here), and it's tricky for vaccine manufacturers. So seasons where that strain dominates tend to be more severe. But now, the CDC says, the proportion of people with H1N1 and B viruses is starting to increase.