Flu vaccine drives can prevent potentially deadly influenza outbreaks in nursing homes but only if both residents and staff are immunized, U.S. researchers reported on Wednesday.
Vaccinating elderly residents alone did not decrease the number of flu outbreaks, nor did vaccinating staff alone, the study by the nonprofit Rand Corporation found.
But if more than 55 percent of the staff and more than 89 percent of the residents were vaccinated for influenza, outbreaks of influenza-like-illness were reduced by 60 percent, the study said.
"Simply immunizing nursing home residents against influenza is not going to ensure they're protected from getting the flu," said Lisa Shugarman, a RAND researcher who led the study.
"It's only the combination of high rates of immunization for residents and staff that appears to make the difference."
Only about 67 percent of the elderly people who should get flu vaccines every year actually get vaccinated, according to the U.S. Centers for Disease Control and Prevention. Fewer than 40 percent of health care and nursing home workers ever get vaccinated.
Because elderly people have less active immune systems, the flu shot is less effective in preventing infection, although studies suggest it can help prevent the worst complications of flu. Of the estimated 36,000 people who die of flu in an average year in the United States, most are estimated to be more than 65 years old.
"Elderly people's immune systems are simply not as strong as younger adults' and the elderly often have multiple chronic conditions that make the immune system less capable of fighting off other diseases," Shugarman said.
Her team surveyed more than 340 nursing homes across the United States belonging to a single nursing home corporation.
On average, 78.4 percent of residents and 40.8 percent of staff were vaccinated, the Rand researchers found.
Writing in the Journal of the American Medical Directors Association, Shugarman's team said they asked about how many residents and staff were vaccinated for flu and then asked about disease outbreaks.
Usually, flu is diagnosed by symptoms because testing can take time and is expensive, so if a person has an influenza-like illness during flu season -- meaning they have fever, sore throat, muscle aches and other symptoms -- they are counted as a flu case.
This year the CDC recommends that 218 million Americans get flu shots, and says 115 million doses will be available during the flu season. The CDC says 77 million doses have been distributed.