THURSDAY, Feb. 21 (HealthDay News) -- The flu vaccine has fallen markedly short of expectations for older Americans this winter, offering this vulnerable population protection against the most virulent strain of flu virus just 9 percent of the time, U.S. health officials reported Thursday.

Even among the general population, the vaccine's effectiveness was just 56 percent, which is considered slightly below average, according to the latest data from the U.S. Centers for Disease Control and Prevention.

Complicating matters, the 2012-13 season has turned out to be one of the more severe flu seasons in recent years because of the presence of the H3N2 virus -- a strain associated with severe bouts of influenza.

"This was really a worse-than-average flu season," said CDC spokesman Tom Skinner. "It hit the elderly particularly hard. We saw a lot of hospitalizations and, unfortunately, a lot of deaths of the elderly."

"For reasons we don't fully understand, the efficacy rate in those 65 and older against H3N2 was lower than what we would like," he said.

This makes it even more important for the elderly, even if they've been vaccinated, to seek treatment early with antiviral drugs like Tamiflu when they come down with the flu, Skinner said.

Dr. Marc Siegel, associate professor of medicine at NYU Langone Medical Center in New York City, agreed that it's "not an ideal vaccine, but it offers a public health advantage -- it's worth taking."

"The reason this vaccine is not that effective for the elderly is because it's hard for the elderly to mount an immune response," he added.

The vaccine is most effective against influenza B viruses, reaching a level of 67 percent protection both overall and among seniors, the CDC report showed.

"The message is we need better vaccines," Skinner said.

Skinner noted that vaccination is still the best protection against the flu, because even if you get sick the vaccine may make the illness milder.

"If people use these numbers not to get vaccinated, I think that will be a tragedy," Skinner said. "Some protection is certainly better than no protection at all."

The findings were published Feb. 22 in the CDC publication Morbidity and Mortality Weekly Report.

This flu season has caused high hospitalization rates, with seniors accounting for 50 percent of all those admitted for the flu.

"This is the highest hospitalization rate [for seniors] since 2003, and may be the highest ever," Siegel said.

Also, nearly 10 percent of deaths up to Feb. 9 have been attributed to the flu or pneumonia associated with the flu. Again, the elderly were hit the hardest, Skinner said.

Sixty-four children have died from flu this season. That number is precise, because the federal government keeps track of pediatric flu deaths. No such count is kept on adults. Typically, approximately 25,000 Americans die from the flu every year, according to the CDC.

Skinner said this year's flu season started early, but seems to be winding down. "But we'll see if that trend continues," he added.

More information

For more on the flu, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: Tom Skinner, spokesman, U.S. Centers for Disease Control and Prevention; Marc Siegel, M.D., associate professor, medicine, NYU Langone Medical Center, New York City; Feb. 22, 2013, Morbidity and Mortality Weekly Report

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