The team led by Dr Kweon Mi Na of the International Vaccine Institute (IVI) in Seoul reported their findings in Monday's online edition of the Proceedings of the National Academy of Sciences.

The research was sponsored by the governments of South Korea, Sweden and Kuwait.

Better ways of delivering vaccine have long been under study, ranging from orally to inhaled, but all seem to have drawbacks.

Now, Dr Kweon and colleagues say, two doses of influenza vaccine under the tongue of mice primed the animals' immune system to fight off what would have been a deadly dose of flu.

Next, they are turning their attention to people, to see if the under-the-tongue vaccine also prompts a strong immune response.

Placing a couple of drops of liquid under the tongue gets the vaccine directly to mucous membranes and prompts a response both in mucous tissues throughout the body as well as in the immune system itself, the researchers said.

If the findings were replicated in humans, they could pave the way for the development of a new generation of vaccines against respiratory infections including bird flu viruses, said Dr Cecil Czerkinsky, deputy director-general for laboratory science at the institute.

Dr John Clemens, IVI director-general, called the studies an important milestone.

'Sublingual vaccination is an entirely new approach to the delivery of vaccines; this approach offers the possibility of vaccinating against a variety of infections without the risks posed by delivering vaccines with needles,' he said.

ASSOCIATED PRESS, AGENCE FRANCE-PRESSE