This year’s flu shot is doing a startlingly poor job of protecting senior citizens from the harshest strain this season, proving just 9% effective, the government said Thursday.

Health officials don’t know why that is, but it helps explain why so many older people have been hospitalized with the flu this year.

Flu vaccine tends to protect younger people better than older ones and never works as well as other kinds of vaccines. But experts say the preliminary results for seniors highlight an urgent need for a better vaccine.

Overall, the vaccine’s effectiveness is 56%, which means those who got a shot have a 56% lower chance of winding up with the flu. That is nearly as good as other flu seasons, the Centers for Disease Control and Prevention said Thursday.

For those 65 and older, it offers far less protection. It is 27% effective against the three strains in the vaccine—the lowest in about a decade but not far below from what’s expected. But the vaccine did a particularly poor job of protecting older people against the toughest flu bug, which is causing more than three-quarters of the illnesses this year.

Vaccination is recommended for anyone older than 6 months, and health officials stress that some vaccine protection is better than none at all. While it’s likely that older people who were vaccinated are still getting sick, many of them may be experiencing less severe symptoms.

“Year in and year out, the vaccine is the best protection we have,” and vaccinations are still recommended for senior citizens, said CDC flu expert Dr. Joseph Bresee.

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By Mike Stobbe
Associated Press