With the flu season now under way, the National Council on Aging has released results from a survey showing that fewer than one in 10 older adults worry about getting the flu. That’s despite data showing that hospitalization rates are on the rise among people ages 65 and older.

People in the 65-and-older group are more likely to have complications from the flu. The risk is even higher for those with a history of heart disease, stroke, diabetes and high blood pressure.

The new survey found that a third of older adults do not know that someone with a chronic health condition such as heart disease or diabetes are at risk for flu complications. And only 8 percent are concerned about getting the flu.

Last flu season, doctors recorded the highest hospitalization rates for older Americans in recent years, according to the Centers for Disease Control and Prevention. Each year, people ages 65 and older account for about half of all flu-related hospitalizations and 90 percent of flu-related deaths.

The flu vaccine is recommended annually for everyone 6 months and older, and a high-dose flu shot is available for people 65 and older. More than half of survey respondents were unaware of the high-dose option.

“If someone doesn’t get vaccinated and develops the flu, it’s the advanced heart disease and heart failure group we’re concerned about,” said Vincent Bufalino, M.D., of the Advocate Heart Institute in Naperville, Illinois.

“If the heart is already working at 40, 50, 60 percent capacity, it overcompensates and that leads to complications,” he said. “If they get the flu or pneumonia on top of heart failure, they could develop worsening failure.”

CDC data from last flu season show that a third of seniors skipped the flu shot, which is free for people on Medicare.

According to the survey, only half of respondents were confident in their knowledge about the different types of flu shots, including the various flu strains.

“Those viral strains change every year and it is vital for older Americans to get these vaccines as they change,” Bufalino said.

But it’s not just older adults who need the new vaccine each year, he said. Anyone over age 35 with heart disease should be vaccinated.

The flu vaccine is 50 percent to 60 percent effective against the flu, CDC director Tom Frieden, M.D., told reporters at a recent briefing. Mutated versions of the virus arise that can sneak past a vaccinated person’s immune system.

“We track flu viruses as they travel across the globe all year long to help us prepare the best vaccines for the coming U.S. seasons, but influenza is unpredictable,” William Schaffner, M.D., medical director of the National Foundation for Infectious Diseases, said at the briefing.

Even so, a flu shot is still the best defense against the flu, Bufalino said, especially for people with heart disease.