Vaccines have been one of the greatest public health interventions in history. Doctors have developed vaccines to prevent some of the world's most terrible diseases, such as smallpox and polio.

But one of the limitations of vaccines is that they need to be injected with a needle. Vaccines often need more than one dose to be effective. It would be much easier if all vaccines could be given by mouth.  Now scientists think that might be possible.

Microbiologist Todd Klaenhammer from North Carolina State University has spent his career studying the kinds of bacteria that we add to food, such as lactobacillus acidophilus.

"We eat this in yogurt and a lot of different products every day... It's totally safe. You can eat these things at over 100 million per gram," Klaenhammer says.

He and his colleagues realized they could use these food-safe bacteria to "sneak" a vaccine into the gastrointestinal tract without damaging the vaccine's potency.

"If you eat a vaccine, just a pure vaccine, your stomach will degrade it, and it will no longer have any vaccine potential," Klaenhammer says. "But if you can put a vaccine, if you will, inside these food-grade bacteria, the food-grade bacteria can survive passage through the stomach, and then once in the small intestine, they can present a vaccine to what we call the mucosal immunity system."

These cells in the mucous lining of the gastrointestinal tract are a key part of the immune system. When the mucous cells recognize the vaccine-laden bacteria, they signal the rest of the immune system to resist the organism targeted by the vaccine. Klaenhammer says he and his colleagues used this technique to give a vaccine against anthrax to mice in the laboratory, and it was 85 percent effective.

"That was equal to the injectable vaccine," Klaenhammer says. He says one of the advantages to this technique is that it would make storage and distribution of vaccines much, much easier.

"You can take these good bacteria that are capable of producing a vaccine, and you can grow them up, preserve them and literally distribute them in a variety of different formats around the world," he says.

Klaenhammer says it should only be a year or two before he and his colleagues could start testing this technique in humans. His research is published in the Proceedings of the National Academy of Science.