Next week is "flu awareness week", with doctors hoping to improve on the 40% of vulnerable people who were vaccinated last year.

But some health authorities claim that the campaign could be compromised by "patchy" supplies of the flu vaccine.

Between 3,000 and 4,000 people die each year from illnesses which can be either fully, or partly blamed on flu infections.

Many elderly or sick people will suffer from flu, then, while weak, fall prey to a secondary infection, such as pneumonia, which proves fatal.

Prof Liam Donaldson: "There's no point in giving a jab to the whole population"

Professor Liam Donaldson, launching the campaign, outlined exactly who should get the jab on the NHS.

Those most at risk are those over the age of 75, or those living in residential nursing homes.

The key risk groups are people with:

• Chronic respiratory illness such as asthma or bronchitis
• Chronic renal disease
• Heart disease sufferers
• Diabetes patients
• People with suppressed immune systems

Professor Donaldson said: "We know that not enough people in these risk groups have been immunised each year.

'No problem for healthy'

"While the occasional bout of flu is not a serious matter for most healthy people, it can lead to serious complications such as pneumonia or bronchitis for others.

"I'm asking people to think about family or friends who may need the vaccine."

He said that younger, fitter people who have flu jabs may be sacrificing longer term immunity from the disease for short term benefits.

He said: "There is no point really giving the jab to the whole population because the immunity you get is quite short-lived."

Avon Health Authority has complained that the supply of vaccines has been "patchy" this year, but Professor Donaldson said that the way the scheme was organised made it less efficient than childhood vaccination programmes.

Instead of being personally invited to come for innoculation, patients attend GP surgeries on their own initiative, meaning the precise number of required jabs is not known.