MONDAY, Jan. 8, 2018 (HealthDay News) -- The current flu season is shaping up to be a nasty one, but there's good news for American seniors who've gotten their flu shot.
New research shows that for older adults, faithfully getting the vaccine each year greatly reduces the odds of catching a flu so severe that it lands you in the hospital.
Researchers found that repeated influenza vaccination offers a double benefit in older adults, proving 74 percent effective in preventing intensive-care (ICU) admissions and 70 percent effective in preventing deaths.
The findings bolster the notion that although getting a flu shot doesn't always prevent the flu, it can make it milder for those who do catch it, said study author Dr. Jesus Castilla. He's a researcher at the Navarra Institute for Health Research in Pamplona, Spain.
"We were surprised by the big magnitude of the vaccine effect in preventing severe influenza," Castilla said. "Our results show the importance of annual vaccination for preventing severe influenza in the older population."
"The prevention of severe influenza was mainly observed in patients repeatedly vaccinated in both the current and previous [flu] seasons, which reinforces the recommendation of annual influenza vaccination in the elderly," he added.
Millions of Americans catch the flu every year, resulting in hundreds of thousands of hospitalizations, according to the U.S. Centers for Disease Control and Prevention. Flu-related deaths ranged from 12,000 to 56,000 annually between 2010 and 2017, according to CDC estimates.
Older adults, whose immune systems aren't as robust, are more prone to suffering severe outcomes from flu infection, including hospitalization, complications and death, Castilla noted.
"Annual vaccination acts as a booster for their immune response," he said. "In other words, the protection increases as compared to the effect of vaccination in a single season."
The new research by Castilla and his colleagues involved hundreds of hospitalized patients, older than 65, who had influenza -- both severe and less severe cases -- as well as those who did not.
People who'd gotten a flu vaccination in the current and three previous flu seasons were half as likely to develop a severe case of the flu, the study found.
"I think it's reassuring that what we recommend people to do -- which is to get vaccinated every year -- actually does provide some additional protection," said Dr. Marci Drees, who was not involved with the new study. She's an infection prevention officer and hospital epidemiologist with Christiana Care Health System in Wilmington, Del.
"The most important take-home message is to get your flu shot and not worry about how effective it is this year," Drees added, referring to concerns that the current U.S. vaccine might be only marginally effective.
"People might be more inclined to skip it, but this study really emphasizes that a primary benefit is year after year of consistently getting that flu shot helps keep people out of the hospital and ICU," she said.
Developing each year's flu vaccine is a tricky business, Drees explained. Health officials in the Northern Hemisphere check what strains of the virus circulated most widely in the Southern Hemisphere in previous months and then adapt the vaccine to those expectations.
"They have to do a little bit of guesswork . . . and don't always guess correctly," she said.
Recent studies show that flu vaccination cuts the risk of flu illness by 40 to 60 percent among the general population.
Drees said she'd like to see research focus on younger populations, including children, to determine if similar protection is conferred after repeated vaccinations.
"You're boosting your immune system every time you get that vaccination," she said. "We know immunity wanes more quickly in older people, so getting that boost year after year is probably contributing to the protection we've seen against severe disease."
The study is published online Jan. 8 in the journal CMAJ.
The U.S. Centers for Disease Control and Prevention has more on flu vaccination.
SOURCES: Jesus Castilla, M.D., Ph.D., researcher, Navarra Institute for Health Research, Pamplona, Spain; Marci Drees, M.D., M.S., infection prevention officer and hospital epidemiologist, Christiana Care Health System, Wilmington, Del.; CMAJ, Jan. 8, 2018, online