It was generally a slow flu season through mid-January and the vaccine was matched well to the predominant strain, and that's what the CDC reported at the prior news conference. More recent data is now available, showing a very recent spike in cases for strains not well matched to the vaccine in the past couple weeks. But the mix could still swing back towards the H1N1 strain, which the vaccine is well matched against.

However, the important question of how beneficial this year's vaccine is despite not being a good match to the recent strains hasn't been answered yet. We don't yet know if vaccinated people are getting some benefit against the H3N2 or B strains or not. Yesterday, the news was reporting all these recent cases of flu and showing full hospital waiting rooms, but we don't know how many were vaccinated or whether they actually have flu or just something that looks like flu. The vaccine does not have to be an exact match to be beneficial but unfortunately, that can't be readily determined until after the fact. That's precisely why the CDC continues to recommend flu shots--in the end, there's a good chance that it will still be beneficial for many people.

At the previous CDC news conference, Dr. Breese mentioned that last season, Department of Defense data showed that when the H3N2 strain that has recently become predominant in the US now was prevalent in Europe, the H3N2 strain in the current vaccine was still 52% protective against it.