Flu jab benefits questioned

Tuesday September 25 2007

Flu vaccinations may not reduce deaths among the elderly, reported the Daily Mail and The Guardian. Usually, it is "claimed that flu jabs halve winter deaths among older people”, said The Guardian, however, “flaws in the studies of the flu vaccine have led them to ‘greatly exaggerate vaccine benefits’.”

The story is based on a review of the literature, which suggests there is still not enough evidence about the benefits of influenza vaccination in the elderly. The researchers call for more high quality studies in elderly people. However, they say that the elderly should continue to receive the flu vaccination whilst this work is carried out.

Where did the story come from?

Drs Lone Simonsen from the National Institute of Allergy and Infectious Diseases and colleagues from other national institutes, health centres, corporations, and universities in the US wrote this review. The authors declared that they had no conflicts of interest and the study was published in the medical journal, Lancet Infectious Diseases.

What kind of scientific study was this?

This was a narrative review of the existing literature about the vaccination of elderly people against influenza. The aim of this review was to highlight the inconsistency of the evidence regarding the effects of flu vaccination on mortality, and “to move towards a better evidence base for the setting of priorities for influenza vaccination and to identify areas where further research is needed”.

A brief description of the methods used to identify the studies was provided; the researchers included all available clinical studies about the effect of the flu vaccination in elderly people on flu-related deaths. They identified these studies using a recent systematic review by the Cochrane collaboration of clinical trials and observational studies, and other available meta-analyses of relevant studies. They report that they searched for English language cohort and observational studies about influenza, but not which databases were used for the search. They found no clinical trials looking at mortality, so they included any placebo controlled trials involving the vaccine.

What were the results of the study?

The researchers highlighted the fact that few placebo-controlled clinical trials of flu vaccines have included elderly people, even though this group is most at risk of flu-related death. They report that although the number of flu vaccinations has increased since 1980, no conclusive evidence has been found to support a reduction in flu-related deaths since this time.

Evidence from cohort studies in elderly people has shown benefit when using the vaccine, but the data is confusing as it has shown that there is a larger reduction in the total risk of death in winter (50% reduction) than the extra number of deaths that influenza is estimated to cause (about 5% each winter). The authors point out that this inconsistency in the data “cannot possibly be correct”, and may be due to bias. Other studies have found that this may be explained by baseline differences in the immunised and non-immunised groups that are compared (selection bias). The authors then suggest methods by which this selection bias could be reduced.

What interpretations did the researchers draw from these results?

The researchers conclude that there is not much evidence to show how much flu vaccination causes a reduction in the number of deaths in elderly people, if at all. They call for further research, in the form of improved observational studies, and randomised controlled trials if possible.

What does the NHS Knowledge Service make of this study?

This was a comprehensive discussion of the controversies surrounding the use of influenza vaccination in the elderly. It highlights gaps in the evidence, and suggests ways that the research might be improved. Importantly, the authors recommend that the elderly continue to be vaccinated against influenza while this research is being conducted.

Sir Muir Gray adds...

Make sure you, or those you love, get the flu jab if you are at high risk.

Analysis by Bazian
Edited by NHS Choices