The world’s population is growing bigger – and older. As we age, our bodies undergo complex changes that, among other things, progressively weaken our ability to respond to infections and develop immunity (this is called immunosenescence). That is why diseases in older adults tend to be more common and severe than those in younger patients, with a greater impact on quality of life, disability, and mortality.
One such disease is influenza, which affects the whole population, but the highest rates of complications and mortality are observed in the elderly (65 years old and above), especially in those who have one or more comorbidities (like diabetes, hypertension and others). Of the 250 000–500 000 influenza-related deaths each year, the elderly account for around 90%. Lower respiratory tract infection, such as pneumonia and bronchitis, is the leading cause of admission to the hospital from infectious diseases and deaths among older adults, with influenza as the most important viral infection clinically.
The fact that vaccines typically do not work as well in older people (because of immunosenescence) presents a challenge, particularly because the illness often results in serious respiratory infections in frail patients such as elderly nursing home residents. Moreover, older people are more likely to suffer from one or more underlying health conditions. As a result, they are also more likely to experience more severe influenza-related complications. Systematic analyses among elderly populations found influenza vaccination – which must be delivered annually, to account for constantly emerging new strains – to be not only successful in protecting people from contracting influenza, but also cost-effective.
A recent large, randomized clinical trial tested whether a flu vaccine with four times the antigen of a standard vaccine could reduce the risk of hospitalization among those especially vulnerable seniors. The results, published in the Lancet Respiratory Medicine, reports that it did so significantly. The study compared hospitalization rates among more than 38,000 residents of 823 nursing homes in 38 states during the 2013-14 flu season based on Medicare claims data. Just under half of the homes, administered the high-dose vaccine while the other provided a standard dose.
Lead author Dr. Stefan Gravenstein, a Professor of Medicine at the Warren Alpert Medical School and Professor of Health Services, Policy and Practice at the School of Public Health at Brown University, said that while a prior study showed that older individuals could respond better to the high-dose vaccine, that study focused on relatively healthy older adults.
“It still needed to be established that it would help even the frailest folks, like those who reside in nursing homes,” Gravenstein said. “In our study, a quarter of the sample was over 90. So, we asked if the high-dose vaccine also would work better than regular-dose vaccine in the population we consider least able to respond. This paper says yes, it can.”
Significant differences were observed in hospital admissions due to any cause (adjusted RR 0.92, 95% CI 0.87-0.97, P=0.003) and hospital admissions related to pneumonia (adjusted RR 0.79, 95% CI 0.27-0.95, P=0.01) among those who received the high-dose vaccine versus those who received standard dose. The risk of hospitalization for respiratory illness, in particular, was nearly 13 percent lower in the high-dose group. That group also had a much lower rate of hospitalization for all causes, respiratory or otherwise, Gravenstein's group said. For many patients, the vaccine appeared to help prevent hospitalization for other problems also, including cardiovascular symptoms.
The study, however, did not find a significant difference in the rate of death. “Nevertheless, a significant reduction in hospitalizations can still be a benefit even though the high-dose vaccine costs more than the standard-dose vaccine”, Gravenstein said. “Especially for older, frail patients”, he said, “reducing trips to the hospital can maintain a higher quality of life”. “The study should provide nursing home leadership with useful information to consider as they plan for future flu seasons”, Gravenstein said.
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