This year’s flu vaccine is not working well. The Centers for Disease Control and Prevention said it’s not a good match for this season’s prominent strain, which has mutated.

So far most of the flu cases this year have been caused by the influenza A H3N2 strain, which is one of the strains included in this year’s vaccine. But the problem is, that strain of the virus has mutated since the vaccine was produced, so it’s not protecting against it.

The CDC sent a warning to doctors about this and reminded them they can and should prescribe antiviral drugs, such as Tamiflu and Relenza, at the first sign of flu infection.

Of the flu virus samples tested, only about half match this year’s vaccine. Since it takes about four months to develop a new vaccine, health officials say it’s too late to make a new, better-matched one for this flu season.

It’s common for viruses to mutate, or “drift,” as they move through the population. The CDC said in a statement that vaccines often provide some protection against drifted viruses. This so-called cross-protection may reduce the severity of the flu and cut down on hospitalizations and deaths.

Infectious disease experts say the H3N2 strain is the most likely to dominate the season because people don’t have much immunity to it, and it will spread more than the strains matched with the vaccine.

Dr. Thomas Frieden, director of the CDC, said H3N2 has historically been a dangerous strain of the flu. In the past, H3N2 outbreaks have caused about twice the rate of hospitalization and death as other flu seasons.

News, Vaccine Injury News Flu Vaccine Not Working Well this Year as Virus Mutates