MONDAY, Feb. 14, 2005 (HealthDay News) -- A sophisticated statistical analysis finds that influenza vaccination is not as effective at reducing deaths among older Americans as the raw numbers might imply.
Study leader Lone Simonsen, a senior epidemiologist at the National Institute of Allergy and Infectious Diseases (NIAID), said the results "suggest that we should vaccinate more people, especially if they are elderly, and that it is important to protect them from influenza in other ways."
The surprising finding appears in the Feb. 14 issue of the Archives of Internal Medicine.
The NIAID study was aimed at clearing up an apparent paradox, Simenson explained. While observational studies have reported that flu vaccination reduces winter deaths for all causes among older people by 50 percent, and vaccination coverage among the elderly increased from about 20 percent before 1980 to 65 percent in 2001, "unexpectedly, estimates of influenza-related mortality in this age group also increased during this period."
So, the epidemiologists got out their calculators and developed "a cyclical regression model" to generate seasonal estimates of influenza-related deaths and all deaths among older Americans for the 33 flu seasons from 1968 to 2001.
Their model showed that excess deaths among people aged 65 to 74 did drop between 1968 and the early 1980s, but that the rate of those deaths has remained the same since then. For people aged 85 and older, "the mortality rate remained flat throughout."
This disconnect can be explained in part by a failure to vaccinate very ill older people, whose fragile health makes them vulnerable when flu strikes, Simonsen said.
In addition to seeking out such older people for vaccination, "we can vaccinate people around them, like caretakers and loved ones in contact with them," she said. Their grandchildren and great-grandchildren can also be vaccinated, Simenson said.
Steps can also be taken to improve the effectiveness of the flu vaccine, she added. For example, some studies have found that injecting the vaccine intradermally -- under the skin -- can produce a better immune response than the current injection method, Simenson said.
Another study in the same journal showed the flu vaccine is highly effective in saving the lives of people under 65 with high-risk medical conditions such as chronic lung disease.
"To our knowledge, this is the first study showing high vaccine effectiveness in reducing severe endpoints such as deaths (78 percent) and hospitalizations for acute respiratory and cardiovascular disease (87 percent) among high-risk persons of working age," wrote researchers at the University Medical Center of Utrecht in the Netherlands.
Their study was a clear-cut endorsement for vaccination of high-risk people of any age. It was based on more than 75,000 observations, 30,000 of them in high-risk persons younger than 65. Similar studies have shown that vaccination against influenza reduce the number of hospitalizations for cardiovascular diseases, as well as for influenza or pneumonia among the elderly, the report said.
"The results of our study lend strong support for the view that all high-risk persons benefit from annual influenza vaccination, regardless of age," they wrote. "Therefore, efforts should be renewed to convince providers and patients of the clinical usefulness of such vaccination, notably among younger high-risk persons."
The two studies are "a fascinating exercise in 'What is truth?'" said Dr. Ted Epperly, a spokesman for the American Academy of Family Physicians.
"What you see in the two papers is a difference between observational and statistical findings," Epperly said. "Statistical studies like this one tend to underestimate vaccination benefits. The Dutch study probably tends to have some overestimation. The truth lies somewhere in between. My belief is that the Dutch paper is closer to the truth than the [NIAID] paper."
As a practicing physician, Epperly said, "I find it hard to believe that the flu vaccine doesn't help. What often pushes older patients over the edge is influenza. The statistical study doesn't jibe with my experience."
U.S. guidelines currently recommend annual vaccination for everyone aged 65 and older, children aged 6 to 23 months, and adults and children with serious medical conditions. Flu shots were rationed for a time this season because of a shortage caused by production problems at a British plant belonging to one of the United States' major vaccine suppliers. However, health authorities now say many doses will actually have to be dumped because demand has slumped.
More information
Flu vaccine recommendations are made by the U.S. Centers for Disease Control and Prevention.
