The mortality benefits of giving elderly people the flu vaccine have been vastly overstated, according to a Review published in The Lancet Infectious Diseases, October edition. Vaccinating people over 65 against influenza in developed countries is aimed at reducing the flu mortality burden.

Dr Lone Simonsen, George Washington University, Washington, DC, USA and team say that vaccinating not-so-frail elderly people more frequently than their frail peers, plus the use of non-specific endpoints, such as all-cause mortality, are the reasons for this exaggeration.

“The remaining evidence base is currently insufficient to indicate the magnitude of the mortality benefit, if any, that elderly people derive from the vaccination program,” say the authors.

Although placebo-controlled randomized trials have demonstrated that the flu vaccine is effective in younger adults, a small number of trials never included the elderly, especially those aged over 70. About 75% of influenza related deaths occur among people aged 70 and over, point out the authors.

These trials suggest that clinical gains and antibody responses in the elderly fall with age after the age of 70.

Even though vaccination coverage rose from 15% in 1980 to 65% today, there has been no confirmation of any influenza-related mortality improvement since 1980, say the authors. “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 say that any future trial should use more precise endpoints, for example, vaccine effectiveness against the highly specific outcome of laboratory-confirmed influenza virus. Even though such a trial would be more expensive and labor intensive, the vaccine efficacy estimates are more likely to be reliable. Rather than use the current arbitrary 4-month period, any future trial should also identify the epidemic period for each season through utilization of actual virus surveillance data.

The writers caution “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.”

“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 randomized 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,” Dr Tom Jefferson and Dr Carlo Di Pietrantonj, Cochrane Vaccines Field, Alessandria, Italy, write in an accompanying Comment.

The Lancet Infectious Diseases
Dr Lone Simonsen, Dr Lisa Jackson
Accompanying Comment
Dr Tom Jefferson, Dr Carlo Di Pietrantonj

Written by: Christian Nordqvist