According to estimates released this morning from the Center for Disease Control and Prevention, this season's flu vaccine was almost completely ineffective in senior citizens.

USA Today reports that this season's flu hospitalization and death rates for Americans over 65 have been higher than ever before seen in this group, with the rate of people in that age group who died of a confirmed case of influenza at 116 per 100,000. The previously highest rate was 90 per 100,000.

For people under 65, receiving the vaccine reduced the need to see a doctor for flu symptoms by at least one-half.

For those over 65, however, the vaccine helped in only 9 percent of cases. The CDC's Weekly Morbidity and Mortality Report was based on a survey of 2,697 children and adults by the U.S. Influenza Vaccine Effectiveness Network from Dec. 3, 2012, through Jan. 19, 2013.

Joe Bresee, chief of the epidemiology and prevention branch of the CDC's influenza division, told USA Today that while the flu this season has been somewhat severe in the general population, "in people over 65 we're seeing a pretty severe year."

"We know that any vaccine, including flu vaccines, is less effective as you get older. We often see lower effectiveness in people over 65, though not always."

The human immune system typically declines in function as people age, making it more difficult for the body to resist viral and bacterial pathogens. While some previous studies have found the flu vaccine to provide a robust benefit for older adults, others indicate less.

The CDC findings match those of European studies on the effectiveness of this season's flu vaccine in Europe. The researchers caution that the findings require further corroboration, since they only looked at people who went to see a doctor for flu symptoms.

The CDC plans to conduct further research to see whether chronic medical conditions and other aging problems may have affected the outcome for the elderly.

Some ways that the flu vaccine can be improved include increasing the dose in order to boost the immune response; adding an adjuvant, a substance that boosts a vaccine's potency; or to simply design better vaccines. These are

This season's vaccine protects against three flu strains: H3N2, influenza B, and H1N1. The vaccine was 67 percent effective against influenza B in adults over 65, but only 9 percent effective against H3N2; there was not enough information about H1N1 to judge its effectiveness.

The vaccine's overall effectiveness for the general population over 6 months old was 56 percent, which is slightly lower than the 62 percent that was projected.

The vaccine's overall effectiveness was:

  • 6 months to 17 years, 58 percent.
  • 18 to 49 years, 46 percent.
  • 50 to 64 years, 50 percent.
  • 65 and older, 9 percent.

Despite these findings, the CDC still recommends that people over 65 get vaccinated. Joe Bresee said, "What we know about people over 65 is that they're at extremely high risk of getting hospitalized or even dying of the flu."

Moreover, people who live and work around people older than 65 are highly recommended to get vaccinated, to make it less likely that they pass along influenza.

The takeaway: even if your grandparents are demoralized by the news of this season's flu vaccine failing their cohort, you should still get vaccinated for their sake.