A needle free way to help lick the forthcoming influenza pandemic has been proposed: "under tongue" vaccination.

We could all be sticking out our tongues at doctors in a few years: as well as helping to appease needle phobic patients, the "sublingual" route could used to protect against a wide range of infections and, as a bonus, generates wider protection in the body.

Joo-Hye Song of the Mucosal Immunology Section, International Vaccine Institute, IVI, Seoul, and colleagues report tests of the method today in the Proceedings of the National Academy of Sciences.

A solution of the vaccine is applied to the floor of the mouth and, thanks to the the high density of blood vessels in the mucous membranes there, immune system cells capture the vaccine and migrate quickly through the body, without the vaccine being degraded, as in the stomach.

Comment: In light of the Signs Supplement: The Flu Vaccine Threat, the reader might not find this such an appealing idea.

Sublingual bio-warfare? No thanks.

The researchers tested the method in mice to determine how well it stimulates immunity, finding that two doses of either live or inactivated flu virus conferred protection against infection.

Researcher Song Joo-Hye and her colleagues at the IVI found that sublingual administration of an experimental flu vaccine is highly effective in protecting mice from influenza virus infection. When the flu vaccine was applied under the tongue, animals developed robust immune responses in their lungs and were fully protected from the disease when later exposed to a severe form of influenza virus.

"These studies provide a basis for further human testing of this alternative form of needle-free vaccination. Aside from its convenience, sublingual vaccination appears to disseminate immunity to a broader range of organs than the classical routes of injecting or ingesting vaccines," says Dr Cecil Czerkinsky, IVI Deputy Director-General for Laboratory Science.

"If these findings are replicated in humans, they could pave the way for the development of a new generation of vaccines that could be used for mass vaccination against enteric, genital, and respiratory infections, including the pandemic avian-human influenza viruses."

A study of sublingual vaccination against cholera has been recently completed in France in 48 healthy human volunteers, in collaboration with scientists from the IVI and from Gothenburg University. "This study used another vaccine (cholera) and showed that sublingual vaccination was well tolerated and gave good mucosal and systemic antibody responses. We plan to initiate a human clinical trial of sublingual flu vaccination in the early fall of 2008."

In addition to negating the need for needles, the sublingual route did not allow viruses to travel into the central nervous system, a rare but potentially harmful complication of intranasal vaccination.

Dr Kweon Mi-na, who oversaw the study, said, "This method of vaccine administration could be safer than nasal administration of the same vaccine using a spray, which is currently the most advanced strategy to vaccinate people against seasonal flu. Sublingual vaccination poses no risk of antigen redirection to the central nervous system."

The researchers suggest that, with further testing, providing influenza vaccines under the tongue could protect people against flu and possible pandemics.

Dr John Clemens, IVI Director-General adds: "These studies are important milestones for the IVI. 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."

The IVI is the world's only international organisation devoted exclusively to developing new vaccines for the poor.