How effective was the 2014-2015 influenza vaccination?

Question

I’m aware that the CDC released this abysmal report on the effectiveness of this year’s influenza vaccination, including data collected through Jan 30, 2015.

In practical terms, this means the flu vaccine reduced a person’s risk of having to seek medical care at a doctor’s office for flu illness by 19%.

However, this is missing much (possibly most) of the flu season. Are there more updated numbers on vaccine effectiveness and/or reports that include data from other (non-U.S.) locales with a similar flu season (i.e. temperate Northern Hemisphere)?

Answer 1

There have been no additional reports in the Morbidity and Mortality Weekly Report, which was where your original article points to regarding the efficacy of the flu vaccine.

However, the most recent update on influenza activity within the United States, which was about a month later than your report, does not suggest there has been any mid-season change in the dominant circulating strains, so the early estimates are likely in the same area.

The one thing that may change this is that a larger number of last season cases of influenza are typically caused by influenza B viruses, as shown in this figure below:

The low effectiveness of the vaccine against the dominant circulating A strains does not necessarily imply a similarly low effectiveness against the later B strains, especially as B strains appear to be somewhat more stable.