FRIDAY, Jan. 9 (HealthDay News) -- If you're over 65, getting a flu shot every year could cut your risk of dying from flu in half, research suggests.

And, even if the vaccine isn't always a perfect match for the strains circulating in any given year, a recent New England Journal of Medicine study that included 10 flu seasons' worth of data also found that an annual vaccine decreases by one-third the risk of hospitalization due to flu complications.

"Most people feel that influenza is a mild disease and one that doesn't cause people to become very ill," said infectious disease specialist Dr. Michael Ison, of Northwestern Memorial Hospital in Chicago. "But it can cause serious complications, and the majority of hospitalizations and illness is in people greater than 65."

Every year, between 5 percent and 20 percent of the U.S. population is infected with the flu virus, according to estimates from the U.S. Centers for Disease Control and Prevention. And, far from being a mild annoyance, flu is responsible for more than 200,000 hospitalizations and about 36,000 deaths every year, according to the CDC.

To prevent some of these illnesses and deaths, the CDC recommends that many groups be vaccinated against the flu each year, including:

• Pregnant women.
• Children -- from 6 months to 5 years of age.
• Anyone over age 50.
• People with chronic medical conditions.
• People who live in nursing homes or any other type of long-term care facility.
• Caregivers of anyone listed above.
• Health-care workers.

The best time to get the vaccine is in the early fall, according to Dr. Robert Schwartz, chairman of family medicine and community health at the Miller School of Medicine at the University of Miami. But both Schwartz and Ison said getting a flu shot even well into winter can be effective.

"Sometimes, people wait until there's an outbreak, but that's not a good idea because it takes about two weeks to develop immunity," Schwartz said.

Previous research, published in The Lancet Infectious Diseases journal, suggested that the flu vaccine might not be that helpful for older people, particularly those in poor health. The study authors suggested that past research had found an advantage in immunized elderly people simply because healthier seniors may be the ones who choose to be vaccinated.

However, the New England Journal of Medicine study cast doubt on those assertions. This study included more than 400,000 people over age 65 who'd been vaccinated and 300,000 seniors who hadn't been vaccinated. All the study participants lived on their own, not in nursing homes or other long-term care facilities.

Those who received a vaccine were 27 percent less likely to be hospitalized due to flu complications, compared to the unvaccinated. And, the death rate was 48 percent lower for those who received the annual flu shot, according to the study.

"It's important to get the vaccine on an annual basis to protect against influenza," said Ison. "Even in years the vaccine is not a perfect match, it may prevent you from getting as sick."

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