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Headline: CDC: Flu vaccine 61% effective, but too few adults get it
Robert Roos | News Editor | CIDRAP News | Feb 20, 2014

2319 children and adults were involved in the study. 784 tested positive for flu.
29% of those who had been vaccinated tested positive, vs. 50% of those who tested negative.
This sounds good but it’s not a 61% effectiveness rate; the difference is 21%. They get 61% by dividing 29/50, which just doesn’t make sense. You decrease your risk from 50% to 29% … roughly from a half to just under a third.
Further, of those who had not been vaccinated, there’s only a 50-50 chance of getting the flu.

A stock photo with the article shows a youngish man in a hospital bed with an IV and breathing tube. There’s no claim that this man suffers from flu.

But the truth is, your risk drops from 50% (not vaccinated) to 29% (if vaccinated). That’s  roughly from a half to just under a third. Not at all the same thing. And it’s not known how these findings translate to larger populations. In fact, from everything I can tell, this population is self-selected; there may be a self-selection difference between those who chose to get vaccinated and those who didn’t.