If you get a situation - as we did in Hong Kong a few years ago, where all the chickens were killed, you will have trouble getting enough eggs to make all the vaccine you need

Dr Nigel Higson, Primary Care Virology Group

The egg vaccine also has the disadvantage of being reliant on the supply of eggs, which can run short during a major outbreak.

Austrian researchers have developed a new vaccine which is grown in cells originally derived from the kidneys of African green monkeys.

This is a cell line which has already been shown to be safe and reliable in the manufacture of other vaccines, and is licenced in the US for this purpose.

Trials of the new-style vaccine found it was as effective at making the body produce antibodies against flu viruses as the conventional vaccine.

No serious side-effect of the monkey vaccine were noted.

'Minimising the risks'

Dr Otfried Kistner, who is part of the project, said: "The development represents the newest and most successful approach to influenza vaccine development in 50 years.

"This does not mean that conventional vaccines are bad. The point of our vaccine is to improve it and minimise the risks which may appear."

Dr Nigel Higson, a Sussex GP and member of the Primary Care Virology Group, said that while the incidence of severe egg allergy was "miniscule", moving away from egg-based vaccines was a good idea.

He said: "If you get a situation - as we did in Hong Kong a few years ago, where all the chickens were killed, you will have trouble getting enough eggs to make all the vaccine you need.

"Using a cell line like this - as long as it is pure - is in the long term more reliable."

The UK Government extended its own flu vaccination programme in 2000 in the wake of an outbreak earlier in the year which stretched the NHS.

Everyone over 65 is eligible to receive a flu jab, as well as people with certain chronic medical conditions such as asthma and diabetes which can render them vulnerable to chest infections.

This winter's flu has been far less severe in terms of case numbers than the one which preceded it.