The flu shot this year is reported to be less effective of protecting elder seniors, the most vulnerable age group, said officials with Centers for Disease Control and Prevention.

Officials said the flu vaccine was only 9 percent effective in preventing those 65 and older of contracting the harsh strain of flu responsible for most of this year's illnesses.

"One possible explanation for this is that some older people did not mount an effective immune response to the H3N2 component of this season's vaccine," the report said. "However, it's not possible to say that for sure."

Dr. Thomas Frieden, the CDC's director said in a congressional hearing this month that in recent years about twice as many elder people has been hospitalized with flu symptoms.

"It seems that this year's flu vaccine is not nearly as effective as we would like among people over the age of 65 for one particular strain of flu," Frieden said Thursday. "That's why early treatment is so important."

Officials did mention that seniors, those 65 and older, should receive their vaccine yearly as they are at high risk of serious illness, hospitalization and death from the flue.

"This flu season has been worse than average and particularly severe for the elderly," Frieden said. "Although it's far from perfect, flu vaccination is by far the best tool we have to protect from the flu."

"Clearly the influenza vaccine world is in a state of rather significant transition -- one from where we overstated the effectiveness of the vaccine and now one where we're confronted head on with the scientific data which says that the impact is at best moderate for most age groups and in some age groups significantly below that which had been previously stated," said Dr. Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.

"We simply need a better vaccine against influenza, one that works better and lasts longer," Frieden said. The Department of Health and Human Services as well as the private sector are working on such a project, he said.

The latest numbers released Friday by the CDC reveals, "influenza activity remained elevated in the United States, but decreased in most areas."