Flu vaccination, which costs the government around £150m a year, may not after all save the lives of the older people who are the target of intensive annual campaigns, according to scientists.

A major review published online today concludes that flaws in the studies of the flu vaccine have led them to "greatly exaggerate vaccine benefits". The authors of the report, in the medical journal the Lancet Infectious Diseases, add that there is not enough other evidence to work out to what extent flu jabs cut the death toll, if indeed they reduce it at all.

The annual flu vaccination campaign, which begins this month, targets people over 65 and those who have long-term health problems. Flu deaths usually peak in January or February.

It is usually claimed that flu jabs halve winter deaths among older people. But Lone Simonsen from George Washington University in Washington DC and colleagues write today that this statistic cannot possibly be correct. Flu is only responsible for 5% of winter deaths in older people.

"We find it peculiar that the claims that influenza vaccination can prevent half - or more - of all winter deaths in elderly people have not been more vigorously debated," they write. "That influenza vaccination can prevent 10 times as many deaths as the disease itself causes is not plausible."

The biggest problem with the flu vaccine studies, they say, is that they have not been carried out on large numbers of the frailer and older members of the population. Those over 70 and in poor health are most at risk. They account for three-quarters of flu deaths.

But most of the studies carried out to discover whether the vaccine worked "by giving equal numbers of people either the vaccine or a dummy vaccine" enrolled only relatively healthy people under the age of 70. The largest and best of these trials, in the Netherlands in the early 1990s, found that among the oldest patients the vaccine's efficacy dropped to just 23%.

Dr Simonsen and colleagues suggest this may be due to a decline in immune response late in life.

A further piece of research found that over-65s produced only half or a quarter of the antibodies to flu vaccines that younger people did. Vaccination coverage has risen steeply in the US, from 15% of the target population in 1980 to 65% today, they write. But there has been no matching drop in influenza deaths.

The review authors say more evidence is needed to determine whether flu jabs are beneficial for older people, but in the meantime the jabs should continue because "even a partly effective vaccine would be better than no vaccine at all".

In a statement the Department of Health did not dispute the findings. It said: "The aim of our influenza policy is to protect those who are most at risk of serious illness or death should they develop influenza ... UK policy is constantly under review to take into consideration all available evidence.

"This study acknowledges that whilst awaiting for an improved evidence base vaccination with flu vaccine in this group should continue."

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