Over the years, the CDC’s Advisory Committee on Immunization Practices (ACIP) has greatly increased the scope of the population for whom it recommends to receive an influenza vaccination. Currently, ACIP recommends that all children 6–59 months old, all health care workers, and all persons aged over 50–in addition to many other groups–should receive an annual flu shot.
However, MedPageToday reports (“…little mortality benefit…“) on an research by Simonsen et al. (2007) in The Lancet Infectious Disease journal. The Simonsen paper claims that influenza vaccination may be saving fewer lives than once thought among older adults.
The reason is that estimates of a 50% or greater reduction in all-cause mortality have emerged from cohort studies fraught with selection bias, asserted a review article in the October issue of The Lancet Infectious Diseases.
But the real effect with flu shots for those 65 and older during December through March could not have been any greater than 5% to 10%, said Lone Simonsen, Ph.D., of George Washington University here, and colleagues. That’s the flu-related mortality burden found in studies of excess all-cause mortality.
Aside from these cohort studies, the evidence is too weak to show any mortality benefit in older adults, who account for 90% of influenza deaths each year, Dr. Simonsen and colleagues added.
Why have other studies found that influenza vaccination had such a large effect of decreased mortality. Seriously ill people are less likely to get influenza shots; they have more immediate medical worries. These people are also more likely to die. Thus, we have a spurious, non-causal relationship between influenza vaccination and mortality due to selection bias.
The authors of the study wisely state the following:
“We must never again allow layers of poor research to mask substantial uncertainty about the effects of a public-health intervention and present a falsely optimistic view of policy,” they wrote. They called for placebo-controlled trials.