Sep 23, 2005 (CIDRAP News) – Researchers who reviewed 64 studies report that influenza vaccination is only modestly beneficial for elderly people overall, with nursing home residents benefiting more than people living on their own.
"Our findings show that, according to reliable evidence, the effectiveness of trivalent inactivated influenza vaccines in elderly individuals is modest, irrespective of setting, outcome, population, and study design," says the report by Tom Jefferson and four colleagues, of the Cochrane Vaccines Field, based in Alessandria, Italy. The study was published online yesterday by The Lancet.
The researchers found that flu vaccines, when well matched to circulating flu strains, reduced the risk of hospitalization for flu or pneumonia by 45% for elderly (65 or older) nursing home residents. For people living at home, flu vaccines were 26% effective in preventing hospitalization for flu or pneumonia. However, vaccination didn't significantly lower the risk of laboratory-confirmed influenza in either group.
The team searched five databases for studies of the effectiveness of flu vaccine in preventing influenza, flu-like illnesses, and related hospital admissions, complications, and death. They found 64 studies from the past four decades, including five randomized trials, 49 cohort studies, and 10 case-control studies, that met their criteria.
For elderly residents of nursing homes who received vaccines well matched to circulating flu strains, the vaccines yielded risk reductions of 23% for flu-like illness, 46% for pneumonia, 45% for hospitalization for flu or pneumonia, 42% for death from flu or pneumonia, and 60% for death from any cause. However, vaccination yielded no significant benefit when the match with circulating flu strains was poor or unknown.
The benefits were smaller for elderly people living in the community, according to the authors' analysis of 20 cohort studies. Vaccines didn't significantly reduce the participants' risk for flu, flu-like illness, or pneumonia. With well-matched vaccines, risk reductions were 26% for hospitalization for flu or pneumonia and 42% for all-cause mortality. Vaccines did not reduce the risk of hospitalization for heart disease or the risk of death from respiratory disease.
However, vaccination looked somewhat more beneficial for community dwellers when the authors adjusted for confounding variables, including sex, age, smoking, and other illnesses. In that analysis, vaccines reduced the risk of all-cause mortality by 47% and lowered the risk of hospitalization by 24% for heart disease and 22% for respiratory diseases.
The authors write that no firm conclusions could be drawn from the five randomized controlled trials they analyzed. However, in analyzing the two trials that had "adequate" randomization and blinding, they found that vaccines were 43% effective in preventing flu-like illness and 58% effective against flu in community-dwelling older people
The study's main findings show somewhat smaller benefits than those cited by the Centers for Disease Control and Prevention (CDC). Information on the CDC Web site says that for older people in nursing homes, flu immunization can be 50% to 60% effective in preventing flu-related hospitalization or pneumonia and 80% effective in preventing flu-related death. Also, the CDC says that community dwelling older people who get flu shots can lower their risk of hospitalization for pneumonia or flu by 30% to 70%.
In response to the new study, the CDC issued a statement today emphasizing that vaccination remains the best way to protect older people from flu and its complications. The agency acknowledged that flu vaccines are not 100% effective and that older people and those with chronic diseases may develop less immunity than healthy young adults.
The CDC said the finding that flu vaccination is more effective for nursing-home residents than for community-dwelling older people "is unexpected and not consistent with other data, including information on immune response to vaccination."
The study authors write that on the basis of their findings, "We believe efforts should be concentrated on achieving high vaccination coverage in long-term care facilities coupled with a systematic assessment of the effect of such a policy. One possible way to improve this strategy might involve the vaccination of carers [caregivers] in an effort to reduce transmission."
The federal government took steps in that direction last month, announcing that nursing homes that serve Medicare recipients would be required to offer flu shots to residents. The government also wants to increase vaccination coverage for nursing home staff members, but there are no plans to require vaccination for them.
The new report was published little more than a week after the CDC urged older people and others in high-risk groups to get their flu shots soon. The agency has recommended that flu shots be reserved for the high-risk groups until Oct 24.
Jefferson T, Rivetti D, Rivetti A, et al. Efficacy and effectiveness of influenza vaccines in elderly people: a systematic review. Lancet 2005;Sep 22 (early online pubication)
CDC information on efficacy and effectiveness of flu vaccine