ATLANTA (AP) — It turns out this year's flu shot is doing a startlingly dismal job of protecting senior citizens, the most vulnerable age group.
The vaccine is proving only 9 percent effective in people 65 and older against the harsh strain of the flu that is predominant this season, the federal Centers for Disease Control and Prevention said Thursday.
Health officials are baffled as to why. But the findings help explain why so many older people have been hospitalized with the flu this year.
Despite the findings, the CDC stood by its recommendation that everyone over 6 months old get vaccinated, the elderly included, because some protection is better than none, and because those who are vaccinated and still get sick may suffer less severe symptoms.
“Year in and year out, the vaccine is the best protection we have,” said Dr. Joseph Bresee, the CDC's flu expert.
Overall, across the age groups studied, the vaccine's effectiveness was found to be a moderate 56 percent, which means that those who got vaccinated had a 56 percent lower chance of winding up at the doctor with the flu. That is somewhat worse than than in other years.
For people 65 and older, the vaccine was only 27 percent effective against the three strains it was designed to protect against, the lowest level in about a decade. It did a particularly poor job against the tough strain that is causing more than three-quarters of the illnesses this flu season.
It is well known that flu vaccine tends to protect younger people better than older ones. Elderly people have weaker immune systems that don't respond as well to flu shots, and they are more vulnerable to the illness and its complications, such as pneumonia.
But health officials said they didn't know why this year's vaccine did so poorly in that age group.
One theory, as yet not proved, is that older people's immune systems were accustomed to the strains in the past two years and had more trouble switching gears to handle this year's different, harsh strain.
The preliminary findings for senior citizens were less than definitive. They were based on fewer than 300 people scattered among five states.
But it will no doubt surprise many people that the effectiveness is that low, said Michael Osterholm, a University of Minnesota expert on infectious diseases who has tried to draw attention to the need for a more effective flu vaccine.
Among infectious diseases, influenza is considered one of the nation's leading killers. On average during the flu season, about 24,000 Americans die of flu, the CDC says.
This flu season started in early December, a month earlier than usual, and peaked by the end of 2012. Hospitalization rates for people 65 and older have been some of the highest in a decade: 146 per 100,000 people.
A high-dose version of the flu shot was recently made available for people 65 and older, but the study was too small to show whether that has made a difference.
The CDC estimates are based on about 2,700 people who got sick in December and January. The researchers traced back to see who had gotten vaccinated and who hadn't. An earlier, smaller study put the vaccine's overall effectiveness at 62 percent, but other factors that might have influenced that figure weren't taken into account.
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