Flu shot may not be enough protection this season

"Get your flu shot." It's the most common health advice this time of year. Physicians and public health officials constantly stress the importance of protecting yourself from the seasonal flu, an illness that kills thousands of Americans every year.

But now the U.S. Centers for Disease Control and Prevention says this year's vaccine may not offer protection from a strain of the bug that's currently making the rounds. According a CDC health advisory released Wednesday, only 48 percent of flu virus samples taken through last month were closely related to this year's North American vaccine.

"It's not going to be as effective as it has been in previous years," CBS News medical contributor Dr. Holly Phillips, told "CBS This Morning." "Basically, what the CDC found was that the predominant strain circulating right now is one called H3N2, and just under half of the samples that they tested were a good match with the vaccine. What that means is that the virus has shifted, or what we call viral drift. It's mutated in some way."

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