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RAND study finds vaccination of nursing home staff, residents, key to reducing flu outbreak

November 16, 2006

Potentially deadly influenza outbreaks in nursing homes are less likely to occur when large numbers of staff and residents get flu shots, according to a study issued today by the RAND Corporation.

The study by the nonprofit research organization found that nursing homes were 60 percent less likely to have a cluster of influenza-like illness cases if more than 55 percent of the staff and more than 89 percent of the residents were vaccinated for influenza.

Researchers defined clusters of influenza-like illness as more than three cases with influenza-like symptoms reported within 72 hours in close proximity within the nursing home.

"Simply immunizing nursing home residents against influenza is not going to ensure they're protected from getting the flu," said Lisa R. Shugarman, a RAND researcher and lead author of the study. "It's only the combination of high rates of immunization for residents and staff that appears to make the difference."

The RAND Health study - titled "The Influence of Staff and Resident Immunization Rates on Influenza-like Illness Outbreaks in Nursing Homes" - appears in the Nov. 15 issue of the Journal of the American Medical Directors Association.

Influenza outbreaks in nursing homes are common and can result in prolonged hospitalizations and death for vulnerable elderly residents, particularly those with serious chronic health problems.

From 1979 to 2000, influenza hospitalization rates for elderly patients were 17 times higher than the average rate, and more than 90 percent of the patients who died were elderly. According to another study, nursing home residents age 65 and older were three times more likely to be hospitalized for influenza than people of similar ages who did not live in nursing homes.

The influenza vaccine can be 86 percent effective for healthy adults when the vaccine matches the prevailing influenza strain. However, studies have shown that the vaccine is less effective among the elderly. In nursing homes, it's estimated to be only 23 percent effective against influenza-like illnesses for residents, and not significantly effective against influenza.

"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.

In fact, Shugarman and her colleagues were unable to validate that immunization rates of residents had any impact on rates of influenza-like illnesses or hospitalizations in their study. Nor were staff vaccination rates on their own a significant predictor. Only if both staff and resident immunization rates were high did the likelihood of influenza-like illness cases and hospitalizations decrease.

Researchers surveyed more than 340 nursing homes belonging to a single nursing home corporation with facilities located across the United States. Ninety percent responded, for a final sample size of 301 nursing homes. The facilities ranged in size from 34 beds to 355. Vaccination status was self-reported and not verified by medical abstraction or review of records at the nursing homes.

Only a third of the facilities tested patients for influenza after they developed influenza-like symptoms.

"Many nursing homes find it impractical to test residents because the tests are expensive, and the results typically would not alter the course of medical treatment," Shugarman said.

As a result, researchers asked how many residents were diagnosed with influenza-like symptoms. These consist of a sudden onset of fever or complaints of feverishness, and at least one respiratory symptom such as sore throat, runny nose, cough or nasal congestion.

The survey focused on influenza-like illness clusters during the October 2004 to May 2005 influenza season, which was distinguished by the fact that the most common strain of the virus was not covered by the vaccine given that season. The average immunization rate was 78.4 percent for residents, and 40.8 percent for staff.

More than a third of the nursing homes -102 of 301 - reported an influenza-like illness cluster. Of those that did, the average cluster was more than 15 residents and the average number of hospitalizations was 2.2, with an average of less than 1 death per facility.

Researchers also found that nursing homes with no influenza-like illness clusters were more likely to have large numbers of Medicaid-eligible patients, an unusual finding that warrants further study, Shugarman said.

There is increasing support in the medical community for encouraging health care workers to be vaccinated against influenza, including recommendations from the Joint Commission on Accreditation of Healthcare Organizations.

But if future studies confirm the results of this one, Shugarman said more forceful requirements may be needed. Educating staff to be sure they know the problems that outbreaks can cause or providing some incentives to get immunized may be useful strategies. Publishing a nursing home's staff immunization rates so that residents' family members can compare facilities also might be a way of increasing vaccination rates for staff.

The study also has implications for healthy adults who want to stay well and for public health efforts to limit the severity of influenza outbreaks, which can put additional strain on an already overburdened health care system.

"Low-cost public health measures such as hand-washing and social distancing - measures that decrease the frequency of close contact with other people, particularly those known to be sick- are just as valid as they ever were," Shugarman said. "People should not be lulled into a false sense of security by getting a flu shot."

RAND Corporation