We have some updates from the CDC regarding this year's activity, as well as some early estimates of vaccine efficacy.
It appears that, consistent with reports in the lay press, this is a more severe year for influenza than the past few years. This is likely due to the dominance of influenza A H3N2 strains in the country, which usually have a tendency to cause more severe disease and have lower vaccine efficacy in prevention. More recently, however, we are seeing an increase in A H1N1 and influenza B strains, for which vaccine efficacy usually is higher. Overall rates of influenza-like illness may be plateauing now, a hopeful sign for a downturn in rates. Regardless, it isn't too late to immunize.
Here's the graph of percentage of visits for influenza-like illness, compared to previous years, for the period ending February 10:
We also have some early estimates of vaccine efficacy available, though it should be noted that these are preliminary and in past years have differed somewhat from the final estimates. Noteworthy is a very low rate of efficacy for A(H3N2) in children 9-17 years of age. Here's the entire table from the February 16 edition of MMWR.
