ATLANTA—A statistical analysis of mortality between 1976 and 1999 found a significant increase in flu-related deaths and to a lesser extent, deaths related to respiratory syncytial virus (RSV).[1] Adults 65 and older had the highest influenza- and RSV-related mortality; within this age-group, the risk of death was greatest for those 85 and older.

The analysis, performed by researchers at the CDC, used national viral surveillance data to arrive at age-specific estimates of deaths attributable to influenza and RSV. They concluded that the increasing mortality from these two diseases can largely be attributed to the increasing age of the population.

INFLUENZA AND RSV MORTALITY

From 1976 to 1998, there was an annual mean of 2,126,740 deaths, of which 1,135,724 were attributed to underlying respiratory and circulatory conditions and 69,140 were specifically attributed to underlying pneumonia or influenza. During the interval studied, the number of underlying pneumonia and influenza deaths increased by 83%, while underlying respiratory and circulatory deaths increased by 11% and 28%, respectively.

Employing a regression analysis that used viral isolate data to measure the circulation and intensity of RSV and influenza, the investigators calculated that an annual mean of 36,155 deaths was attributable to influenza. However, this number varied widely each year, from a low of 17, 056 to a high of 51,296.

RSV was associated with an annual mean of 11,321 deaths; this number did not vary much from year to year. “When you look at circulation patterns,” said William W. Thompson, PhD, an epidemiologist with the Immunization Safety Branch of the National Immunization Program at the CDC, “RSV has a clear seasonal pattern. It’s predictable—much more so than influenza.”

OLDEST AT RISK

Although young children have an increased risk of death from influenza and RSV, 90% of influenza-related deaths and 88% of RSV-related deaths occurred in people 65 and older (Table 1). Between 1976 and 1999, the number of people 65 and older rose significantly; this increase in the elderly population explains much of the growth in the death rates from influenza and RSV.

Among the elderly, the risk of dying from influenza or RSV rose exponentially with advancing age. Those 85 or older were 16 to 32 times more likely to die from influenza than were those between 65 and 69.

In the current study, RSV was the most common viral cause of death in children younger than 5. However, RSV-related mortality was highest in the elderly, and significantly more RSV deaths occurred among elderly people than among young children.

“RSV is hard to detect in the elderly, because it’s more difficult to isolate the virus,” said Dr. Thompson. “Generally speaking,” he continued, “in an elderly person, influenza is generally assumed instead of RSV.” Dr. Thompson noted that a vaccine for RSV is currently under development.

INFLUENZA VACCINE

One preventive measure currently available is the influenza vaccine. However, the effectiveness of the vaccine is significantly lower in elderly patients. “It has been long known that the influenza vaccine works less well in people over 65,” said David M. Morens, MD, a medical epidemiologist at the NIH. “Simply put, when you get older, the vaccine works less well. It works much less well at 75 and even worse at 85.”

Why doesn’t the vaccine work as well in the elderly? Dr. Morens admitted that the medical community does not know precisely, but there is definitely a problem with immunogenicity. “It has always been taught that the influenza vaccine is about 70% effective in people over the age of 65. In reality, it’s probably less than that.”

It’s important to look carefully at efficacy, said Dr. Morens. “Does the vaccine prevent the flu? It won’t necessarily prevent it in the elderly. Does it prevent severe or fatal flu-related diseases? There is some evidence that even if the vaccine doesn’t prevent infection, it does prevent death.”

To that end, there is a need for better vaccines, as well as vaccination administration strategies. “My opinion is that … when trying out new vaccine strategies, the eldest elderly should be used as a litmus test for efficacy.”

A PUBLIC HEALTH PROBLEM

In an editorial,[2] Dr. Morens noted that the life expectancy for 65-year-old men and women currently exceeds 81 and 84 years, respectively, and is increasing. He also pointed out that current influenza prevention strategies tend to consider people 65 and older as a single risk group.

Dr. Morens questioned the effectiveness of current influenza-prevention approaches that are centered more on the individual than the community. People’s feelings about vaccination present another hurdle. “There is strong [sentiment] against the influenza vaccine,” said Dr. Morens. “That this happened signifies a failure in public health leadership. The notion that you can get the flu from the vaccine is one of those things that got into the public domain and has taken on a life of its own.”

Locally, doctors, nurses, and health care providers should do what they can to educate people about the importance of immunization, Dr. Morens suggested. “However,” he stressed, “leadership has to come from national agencies. These agencies should be much more aggressive in promoting vaccination.”

Dr. Morens called the aging of the baby boom generation “an impending public health disaster of great proportion.” Still, he added, despite their imperfections, influenza vaccines currently represent the chief means of reducing the risk of influenza-related death, hospitalization, and illness.

—Gale Jurasek

References
1. Thompson WW, Shay DK, Weintraub E, et al. Mortality associated with influenza and respiratory syncytial virus in the United States. JAMA. 2003;289:179-186.
2. Morens DM. Influenza-related mortality: considerations for practice and public health. JAMA. 2003;289:227-228.

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