MONDAY, Jan. 28 (HealthDay News) -- A drop of vaccine placed under the tongue might one day ward off the flu.

Not only would the new method, so far tested only in mice, be more convenient, it also appears to be more effective than the flu shot or nasal spray, the South Korean researchers noted.

"This has the potential to be widely accepted by people who are afraid of needles, but it's clearly an introductory study and needs to be further studied in humans," said Dr. William Reisacher, an assistant professor of otolaryngology at Weill Cornell Medical College in New York City.

And in developing countries, there is another advantage: indirect prevention of other diseases.

"Sublingual [under the tongue] vaccination elicits broad spectrums of systemic and mucosal immunity. This route is needle-free so that developing countries' people would most benefit to avoid contamination/infection by reused needles," said study senior author Mi-Na Kweon, chief of the Mucosal Immunology Section at the International Vaccine Institute in Seoul.

And according to Kweon, whose study was in this week's issue of the Proceedings of the National Academy of Sciences, "several clinical trials using sublingual route are now ongoing so that it might be not so far away for humans."

Most flu vaccines are delivered via injection, though recently a nasal spray (FluMist) has become available. The flu shot, which contains killed virus, is approved for use in people older than 6 months. The nasal spray is made with live but weakened flu viruses, and is approved for healthy people aged 2 to 49 who are not pregnant.

According to background information in the study, most environmental pathogens, such as the flu virus, enter the body through the respiratory, gastrointestinal and genital tracts.

The sublingual vaccine would provide protection at the point of entry, so to speak. And unlike other oral vaccines, it would avoid subjecting the vaccine to enzymes and acids in the stomach.

Sublingual therapy is already used for allergy drugs in children, primarily in Europe.

In this study, mice were given two doses of either live or inactivated flu virus two weeks apart. Both delivery methods were effective in stimulating the immune system.

When later exposed to a severe form of influenza virus, the animals were fully protected.

Delivering vaccine under the tongue also prevented viruses from traveling to the central nervous system, which is a rare but dangerous complication of the nasal spray.

"They basically showed that the vaccine was able to affect change in the immune system and protected against the flu," Reisacher said. "It's an effective way of exposing a vaccine to the immune system. With sublingual delivery, the vaccine is not absorbed that rapidly but it is maintained in the lining of the mouth -- the mucosa -- allowing the antigen to be exposed [to the immune system]."

More information

For more on current flu vaccines, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: William Reisacher, M.D., assistant professor, otolaryngology, Weill Cornell Medical College, and director, allergy, New York Presbyterian Hospital, New York City; Mi-Na Kweon, Ph.D., chief, Mucosal Immunology Section, International Vaccine Institute, Seoul, Korea; Jan. 28-Feb. 1, 2008, Proceedings of the National Academy of Sciences

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