Flu shot less effective in 2014 since virus has mutated: CDC

If you are like the many millions of Americans who have already gotten their flu shot this year, new research shows that the current flu vaccine may not be a good match for the most common seasonal flu strain currently circulating in the United States, the U.S. Centers for Disease Control and Prevention said Wednesday in an advisory to doctors.

In an advisory to doctors, the Centers for Disease Control and Prevention said influenza virus samples taken from Oct. 1 through Nov. 22 showed just under half, or 48 percent, matched the current influenza strains in this year's vaccine.

Just over half, 52 percent, of the samples were different, indicating a mutation or drift of the strain. In past seasons when the influenza A (H3N2) strain had mutated from the vaccine strain, flu shots were less effective, the CDC said in the advisory.

In February a panel of experts decided on 3 strains of the virus to include in this year's vaccine. The decision is based on common strains circulating around the globe throughout the year. That information is used to predict which strains will be common during the upcoming flu season.

Researchers try to anticipate which flu strains will spread months before the season starts, but the virus can mutate rapidly and render part of the vaccine ineffective. Still, the Centers for Disease Control and Prevention recommends people get the vaccine because it may lessen the severity if you do contract the virus.

"Though reduced, this cross-protection might reduce the likelihood of severe outcomes such as hospitalization and death," the CDC said, according to NBC News. "In addition, vaccination will offer protection against circulating influenza strains that have not undergone significant antigenic drift from the vaccine viruses."

"The flu is bad, and you want to do anything you can to prevent getting it and to prevent giving it to other people, said Dr. Lisa Thebner, a pediatrician in New York City, according to Fox News. "The vaccine isn't perfect, but it's the best protection we have for prevention."