Annual Flu Shots May Be of Little Benefit to the Elderly

After years of telling patients with diabetes that they need to get flu shots, we now are learning that the elderly may receive little to no benefit from annual influenza vaccinations, according to a review of current evidence study. 

"Influenza vaccination policy in most high-income countries attempts to reduce the mortality burden of influenza by targeting people aged at least 65 years for vaccination," write Lone Simonsen, from George Washington University in Washington, DC, and colleagues. "However, the effectiveness of this strategy is under debate. Although placebo-controlled randomized trials show influenza vaccine is effective in younger adults, few trials have included elderly people, and especially those aged at least 70 years."

Nearly every year, winter influenza epidemics in the United States affect approximately 5% to 20% of the population, causing about 300,000 hospitalizations and 36,000 deaths. People aged 65 years and older account for up to 90% of all influenza-related deaths.

In most high-income countries, one of the strategies of vaccination policy against influenza is to target people 65 years of age and older in hopes of decreasing the mortality burden of influenza. However, the apparent benefits of this strategy may have been exaggerated by frailty selection bias, in which healthier elderly are vaccinated more often than frail elderly, as well as by the use of all-cause mortality and other nonspecific trial endpoints.

"Paradoxically, whereas those studies attribute about 5% of all winter deaths to influenza, many cohort studies report a 50% reduction in the total risk of death in winter — a benefit ten times greater than the estimated influenza mortality burden," the authors write. "New studies, however, have shown substantial unadjusted selection bias in previous cohort studies."
This review includes a suggested analytical approach to identify this type of residual bias, which should help elucidate what mortality benefits can and cannot reasonably be expected from influenza vaccination.

The authors recommend use of more specific endpoints in future trials. Recognizing that the aged immune system may not efficiently respond to influenza vaccination should facilitate development of other options for influenza control, such as more immunogenic vaccines or larger doses of vaccine to be used in the elderly, a combination of live and killed vaccine formulations, more aggressive use of antivirals for treatment and prophylaxis, and indirect protection via increased vaccination of transmitter populations. Ongoing evaluation would need to determine the effectiveness of such approaches.

"While awaiting an improved evidence base for influenza vaccine mortality benefits in elderly people, we suggest that this group should continue to be vaccinated against influenza," the authors conclude. "Influenza causes many deaths each year, and even a partly effective vaccine would be better than no vaccine at all. But the evidence base concerning influenza vaccine benefits in elderly people does need to be strengthened."

Source: Diabetes In Control: Lancet Infect Dis. 2007;7:658–666