Under-the-tongue flu vaccine may be most effective

Administering flu vaccines under the tongue may be more effective and offer more protection than injecting or inhaling the drug, a study with mice in South Korea has found.

The base of the mouth is a “very good absorbent and competent tissue ... in taking vaccine and presenting it to the immune system ... to initiate an immune response,” Cecil Czerkinsky, biological sciences professor at the Seoul National University, said in a telephone interview.

There is currently no vaccine that is administered under the tongue, or what is known as the sublingual area. But there have been recent studies testing its effectiveness in inducing immune responses in mucosal tissues in the respiratory system, gut and inside of the cheek, and blood.

In an article published in the Proceedings of the National Academy of Sciences, the researchers described how they administered both live and killed flu vaccines under the tongues of mice and then exposed the rodents a few weeks later to lethal doses of influenza viruses.

“All the mice were protected,” Czerkinsky said, and the vaccines also provided cross-protection against other flu viruses.

Unlike injected vaccines, which induce antibody production mainly in the blood, the sublingual method “induced antibodies in both lungs (mucosal lining) and the blood,” he said.

“Influenza is a mucosal disease.” The sublingual method provides disease protection at the very early stage before it goes to the blood.

Such a method is different from the oral route, often seen as subjecting drugs to the erosive effects of digestive fluids.

The correct way to do it would be for the person to hold the vaccine in the base of the mouth for about 30 seconds.

“In 30 seconds, the sublingual area absorbs the vaccine and immediately the vaccine is taken up and processed by the immune system and it initiates very rapid stimulation of antibodies, within days,” Czerkinsky said.

The study also suggested that this method may be safer than administering vaccines intranasally, or through inhaling.

There are nerve fibers in the nose, which opens up the possibility, however rare, that viruses in vaccines could enter the central nervous system, the researchers said.

Control groups of mice were given vaccines intranasally. The scientists later detected virus in the olfactory nerves of mice that were given vaccines containing killed viruses, which raised safety questions.

Mice that were given vaccines containing live, attenuated virus intranasally all died very quickly.

The scientists plan to conduct a clinical study later this year.