(WVUE/FOX) - U.S. health officials say this year's flu vaccine is even less effective than previously thought.
The shot is showing only 18 percent effectiveness against the dominant H3N2 flu strain. That's a drop from the estimated 23 percent protection prediction made earlier in the season.
Even worse, a Centers for Disease Control and Prevention panel pegged the effectiveness for the injected vaccine for kids between the ages of 2 and 8 at 15 percent.
The poor performance is due to the mutations of the viruses circulating. The CDC says decisions about what to cover in this year's seasonal flu vaccine were made in February of last year. Those choices are made months in advance so manufacturers have time to make enough vaccine.
The mutated strain of H3N2 was only seen for the first time in March of 2014 and didn't become dominant until September.