Doubts cast over benefit of flu jabs for elderly people
Alain Dex, Publiphoto Diffusion/Science Photo Library
Flu immunisation may save fewer lives than expected |
As the annual influenza immunisation campaigns kick off in Britain next week, evidence for the benefits of vaccinating elderly people against flu is questioned in a review article published online in Lancet
Infectious Diseases (24 September 2007).
Lone Simonsen, of the National Institute of Allergy and Infectious Diseases,
Bethesda, Maryland, and colleagues argue that frailty selection bias
and non-specific endpoints, such as all-cause mortality, in cohort studies
have led to greatly inflated estimates of how well vaccination protects
elderly people from flu-related death.
The remaining evidence, they say, is not sufficient to indicate the magnitude
of the mortality benefit, if any, that elderly people derive from the
vaccination programme.
“Although placebo-controlled randomised trials show 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 [in the US],” say
the researchers.
They point out that flu vaccines cannot prevent 50 per cent of all winter
deaths in elderly people, as claimed in cohort studies, since the estimated
burden of excess deaths related to flu is 5 per cent per year in the
US. “That influenza vaccination can prevent 10 times as many deaths
as the disease itself causes is not plausible,” they say.
The researchers highlight studies that suggest vaccine effectiveness
declines sharply after the age of 70 years and that antibody responses
to flu vaccine in elderly people are only about one-quarter to one-half
as strong as those in younger adults.
They propose that it may be time to revisit randomised controlled trials
in elderly populations. However, they add that, while awaiting an improved
evidence base, elderly people should still continue to be vaccinated.
“Influenza causes many deaths every year, and even a partly effective
vaccine would be better than no vaccine at all,” they say.
In an accompanying editorial, Tom Jefferson and Carlo
Di Pietrantonj,
of the Cochrane Vaccines Field, say that, in their opinion, randomised,
placebo-controlled trials are the only ethical and scientific way to
have a definitive answer to the question of whether current flu vaccines
protect elderly people.
However, the trials need to be large enough to detect rare outcomes and
long enough to cover more than one flu season, they say.
This year’s flu campaigns in Britain again target younger people
in at-risk groups as well as those over the age of 65 years. At-risk
groups include people with serious heart or chest complaints (including
asthma), serious kidney or liver disease, diabetes, lowered immunity
due to disease or treatment, multiple sclerosis or other degenerative
conditions of the central nervous system, or anyone who has had a stroke
or transient ischaemic attack.
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