March 12, 1999

Study calls for expanded influenza prevention efforts

Study calls for expanded influenza prevention efforts

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Dr. Marie Griffin

Improving influenza prevention efforts among high-risk young and middle-aged adults could reduce the number of hospitalizations and deaths associated with the virus each year.

In a study published this week in the Journal of the American Medical Association, Vanderbilt University Medical Center researchers report that women under the age of 65 with certain chronic medical conditions experience substantial morbidity and mortality from acute cardiopulmonary events during influenza season each year. These chronic conditions include cardiac or pulmonary disease, diabetes, malignancy, chronic renal disease and HIV infection.

While the vast majority ‹ between 60-90 percent ‹ of people who die during influenza season are 65 years or older, nearly three quarters of pneumonia- and influenza-associated hospitalizations occur among people younger than 65.

The study tracked non-pregnant women under the age of 64 who were enrolled in Tennessee's Medicaid program from 1974-1993.

It was discovered that for every 10,000 women aged 15-44 deemed to be at high-risk, 23 had cardiopulmonary hospitalizations related to influenza each year. Among 10,000 women aged 45-64 years, approximately 58 cardiopulmonary hospitalizations and four deaths were related to influenza each year. In comparison, hospitalizations and deaths among women with no identified high-risk conditions were four per 10,000 among women aged 15-44 and six per 10,000 among women aged 45-64.

"Influenza has an enormous impact because 10 percent of adults and close to 30 percent of school-age children are infected each year," said Dr. Marie R. Griffin, professor of Preventive Medicine and senior author of the study.

This study also provides the first population-based evidence that HIV patients are especially hard hit by influenza. Women with HIV had the highest influenza-attributable risk among the women studied. While the study provides justification for more wide-spread use of influenza vaccine for women with HIV, the authors write that more data are needed to determine if the effects would carry over to the more diverse ‹ and predominantly male ‹ HIV-infected patients in the general population. More data is also needed to determine whether influenza vaccine protects these patients.

Each year in the United States influenza accounts for an estimated 10,000-40,000 deaths, nearly 200,000 hospitalizations and millions of lost work days. The annual economic costs associated with influenza epidemics exceeds $12 billion.

In this retrospective cohort study, researchers used the winter-time when influenza virus was not circulating as a baseline to weed out other environmental or microbial factors that could affect cardiopulmonary hospitalization and death rates. Hospitalizations and deaths that occurred during winter-time when influenza virus was circulating that were in excess of this "baseline" were attributed to influenza.

They found that influenza-attributable risks in patients with diabetes, malignancy and chronic renal disease were comparable with the risks faced by patients with chronic lung or heart disease. What's more, these rates are comparable with previously reported hospitalization and mortality rates in adults older than age 65 who don't have high-risk conditions.

Nationwide, efforts to improve influenza vaccination levels have been a success among persons aged 65 years and older. During the past decade, these levels have improved from 23 percent vaccinated to 66 percent, surpassing the national health objective for the year 2000 of 60 percent.

However, there has been no parallel improvement in vaccination levels among younger high-risk patients, only 30 percent of whom get inoculated each year. The study's authors say that stronger efforts to reach these populations for annual influenza immunization is needed.

"At the very minimum, targeted efforts to improve influenza prevention among high-risk young and middle-aged adults are warranted," they write in the study's conclusions. "Furthermore, these data may be useful in determining the cost-benefit ratio of universal influenza immunization."