The number of states affected by influenza in the U.S. has risen from 44 at the middle of this month to 49, at the end of this week. In addition 22 pediatric deaths have been registered, the U.S. Centers for Disease Control and Prevention reported on Friday.

It’s no longer a secret that this year’s flu vaccine has not been able to cover all the strains of the viruses that had been circulating throughout the United States. Moreover, some of the strains have become immune to antiviral medication: “two of the three common circulating types or subtypes [of viruses] are not as well-covered by the vaccine as an ideal match this year,” Dr. Joe Bresee, chief of the branch of epidemiology and prevention at CDC warned on February 16th.

That’s why the U.S. Food and Drug Administration officials met the CDC officials on Thursday and greed to change next year’s flu vaccine mix.

“We didn't have enough information to know that this was going to be a serious player. In fact, we thought we were going to have a pretty mild season until a few weeks ago,” said CDC flu director Dr. Nancy Cox quote by the Associated Press referring to the ravages made by this year’s influenza strain.

Health officials announced the selection of a new Type A strain known as H1N1-Brisbane/59; A-Brisbane/10, a version of the H3N2 flu; and a newer Type B-Florida for the 2008-2009 flu season.

However, “influenza viruses are changing all the time.” Therefore, health officials cannot be sure if this year’s selection will match the next year’s type of influenza virus. “We're trying to have a window which allows us enough time to manufacture a vaccine. We can't just turn on a dime," said Dr. Norman Baylor, FDA's chief of vaccine review.

The virus strain most common in the U.S. this year is the influenza A H3N2 strain and it’s a strain not included in this year’s vaccine. Moreover, this year’s vaccine is not well-matched against influenza type B.

Almost 8.1 percent of the influenza type A viruses tested by the CDC were resistant to Tamiflu (the antiviral drug made by Roche AG and Gilead Sciences), while less than 1 percent of the viruses have been resistant to the drug in past years.

Although this year’s vaccine isn’t a good match for most of the circulating flu virus, CDC officials still said people should be vaccinated.

Reports indicate that each year, an estimated 2 percent to 20 percent of the U.S. population suffers from the flu. Approximately 200,000 people are hospitalized from flu complications and more than 36,000 people die from influenza, which is especially dangerous for those who are young, old, or have weakened immune system, according to the CDC.