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Cold, Flu, & Cough Health Center

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Flu Vaccine Less Helpful to Seniors

Flu Vaccine Still Advised, but It Offers Elderly Little Pneumonia Protection

Flu Shot Still Advised continued...

But if flu were behind 30% of pneumonia cases during a flu season in which the vaccine were 8% effective against all-cause pneumonia, the flu vaccine would be about 33% effective. That's not great, but much better than no protection at all.

And flu vaccine also prevents the flu -- a miserable illness even if it does not result in pneumonia.

"Nobody suggests we stop vaccinating elderly people against the flu," Shay tells WebMD. "This study doesn't contravene any recommendations for annual vaccination for people in this age group."

Confirming Cases of Flu

The Jackson study did solve one big problem for flu researchers. It looked at the medical records for 1,173 65- to 94-year olds who had the flu during the 2000, 2001, and 2002 flu seasons and compared them to 2,346 age- and health-matched people who did not get the flu.

Because people usually get their flu shots in the fall, well ahead of the usual start of flu season, Jackson's team was able to look at whether people got pneumonia in the period after they got their flu shots but before they could have gotten the flu.

This turned up a revealing phony statistic: The flu vaccine appeared to be 40% effective in preventing all-cause pneumonia, even though it could not have had any effect during that time.

But when the researchers considered several confounding factors, they corrected this false finding. Those factors -- such as asthma, smoking, home use of oxygen, use of inhaled steroids, previous pneumonia episodes, and antibiotic prescriptions -- turned out to be responsible for the false reading. That's because people able to get their flu vaccinations tend to be healthier than those who don't.

After correction, the flu vaccine no longer prevented pneumonia before flu season. And during flu season, it was a statistically insignificant 8% effective in preventing all-cause pneumonia.

That forever changes how flu effectiveness studies should be done, says Shay. It's no longer going to be helpful to study the effects of flu vaccine without accurately identifying who truly got the flu and who did not. Measures such as flu-like illness, hospitalization, or all-cause pneumonia are just too misleading.

"If we are going to move forward, flu-vaccine efficacy studies will need to have lab-confirmed flu as an outcome," Shay says.

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