(CNN) — This year’s flu vaccine is not as effective against the current strain of the influenza virus because the virus has mutated, the U.S. Centers for Disease Control and Prevention said Wednesday in an advisory to doctors.
The advisory said 52% of the 85 influenza virus samples collected and analyzed from October 1 through November 22 were different than the virus strains included in this year’s vaccine, indicating a mutation, or drift, of the strain.
The most common strain of the virus reported so far this season is influenza A (H3N2). In the past this strain has been linked to higher rates of hospitalization and death, especially for those at high risk for complications, which is usually the very young, the elderly and those with chronic health conditions.
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. Some years the vaccine is a better match to the circulating strains than others.
While the vaccine is not as protective against a mutated strain, it can still decrease the severity of illness caused by the virus. It can also protect against other circulating strains of the virus, which is why the CDC still recommends getting vaccinated.
“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. “The vaccine isn’t perfect, but it’s the best protection we have for prevention.”
When asked if people should be concerned, Thebner said “people should always be concerned about the flu.”
In the advisory, the CDC emphasized the importance of treating those at highest risk from complications with the antiviral medications Tamiflu and Relenza, which are considered most effective at reducing complications when given as soon as possible once symptoms begin.
During the 2012-2013 flu season 12,337 people were hospitalized with flu-related illness and 149 children died, according to CDC surveillance data. Ninety percent of those children were unvaccinated.
Overall, flu activity across the country is currently low, according to the latest flu outbreak data from the CDC.