The mortality benefits of vaccinating elderly people against the influenza virus have been greatly exaggerated, conclude authors of a review published in the October edition of The Lancet Infectious Diseases.
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. Dr Lone Simonsen, George Washington University, Washington, DC, USA and colleagues say that frailty selection bias (ie, where not-so-frail elderly people are vaccinated more often than their infirm peers), and the use of non-specific trial endpoints such as all-cause mortality have been the reasons behind this exaggeration. They say: "The remaining evidence base is currently insufficient to indicate the magnitude of the mortality benefit, if any, that elderly people derive from the vaccination programme."
The authors point out that although placebo-controlled randomised trials show the influenza vaccine is effective in younger adults, few trials have included elderly people, and especially those aged at least 70 years, the age-group that accounts for three-quarters of all influenza related deaths. Such trials suggest that clinical benefits and antibody responses in elderly people decline with increasing age past 70 years.
Further, they say that recent excess mortality studies have been unable to confirm a decline in influenza-related mortality since 1980, even as vaccination coverage increased from 15 percent to 65 percent. The authors say: "Paradoxically, whereas those studies attribute about 5 percent of all winter deaths to influenza, many cohort studies report a 50 percent reduction in the total risk of death in winter a benefit ten times greater than the estimated influenza mortality burden."
They propose that future trials should use more specific endpoints, eg. vaccine effectiveness against the highly specific outcome of laboratory-confirmed influenza virus, which although labour intensive and expensive, is more likely to obtain more realistic estimates of vaccine efficacy. Future trials should also identify the epidemic period for each season through use of actual virus surveillance data, rather than the current arbitrary four-month period.
They end with a note of caution, saying: 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. 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.
In an accompanying Comment published Online in The Lancet today, Dr Tom Jefferson and Dr Carlo Di Pietrantonj, Cochrane Vaccines Field, Alessandria, Italy say: If current evidence points to substantial uncertainty, then what next? Simonsen and colleagues suggest that refocusing on the likely complications of immune senescence would require vigorous pursuit of other options. They also confront the ultimate taboo that drew so much scorn in the evidence overview: doing randomised trials in elderly people to settle the issue conclusively. That suggestion, which seems to fly in the face of current policies, is in our opinion the only ethical and scientific way to have definitive answer to the question of whether or not current influenza vaccines protect elderly people.
Journal
The Lancet Infectious Diseases