This year's flu vaccine provided little protection to people 65 and older who got a shot, new data released by the U.S. Centers for Disease Control reveal.
The study estimates how well the vaccine did at preventing people from becoming sick enough to need to see a doctor, preventing "medically attended flu" in influenza science parlance. And the data suggest this year the vaccine didn't perform very well for older adults.
It found that a flu shot cut an older adult's risk of contracting a case of influenza A H3N2 that needed medical care by only nine per cent.
When the scientists calculated the overall effectiveness, the vaccine's ability to prevent medically attended flu caused by both flu A and B viruses, the estimate was 27 per cent for older adults.
The findings are disappointing given the H3N2 component in this year's vaccine is well matched to the viruses circulating. Paradoxically, the B component of the vaccine isn't as closely matched to circulating viruses, yet it is performing better, according to the study.
Dr. Joe Bresee, a flu expert with the CDC, said older adults need to know that if they got a flu shot and they develop flu-like illness, they may have influenza and should see a doctor to determine if they should take antiviral drugs.
"We wanted to make sure that people knew that, especially if you're elderly to know that, because we still want to communicate the fact that if you do get sick, get antivirals. And don't assume just because you got the vaccine, that that flu-like illness you've got can't be flu," said Bresee, who heads the CDC flu division's epidemiology team.
For Canada the H3N2 effectiveness rate was 45 per cent, she noted, while European investigators pegged the effectiveness against that component at 42 per cent.