1. Enough to go around

2. Got antibodies?

4. More than resistance...

Before it was eliminated by vaccines, smallpox killed more people in the 20th century than war. CDC's Emerging Infection's page.

Pity the poor lab techs...
If the idea of swallowing vaccine with a bite of banana troubles you, consider history.

Take British physician Edward Jenner. Two hundred years ago, in what surely ranked among the most vulgar experiments ever, he took pus from scabs of cowpox-infected cows and rubbed it in a cut on a boy's arm. There was a small reaction as the immune system fired up its soldier antibodies -- but the form of the virus in the pus was too weak to cause full disease. Jenner later exposed the boy to the real thing: live smallpox vaccine. Luckily for them -- and the millions who have since benefited from vaccination -- the boy was immune.

Jenner's daring experiment became a model for modern vaccines like smallpox and polio, where weakened (attenuated) forms of viruses trigger an immune response, but not the disease. These whole organism vaccines, however, carry the small risk that the microorganisms will bring on a full-fledged disease state. For that reason, vaccine makers now favor so-called sub-unit preparations, made mostly of individual proteins from the germ. The immune system roots out this antigen, learning to recognize the pathogen in the process. Left behind, an army of sentinel cells is forever on alert, ready to be unleashed if the pathogen ever returns. But sub-unit vaccines carry their own set of complications. Antigens are expensive to produce, require refrigeration, and degenerate in the stomach unless protected.

A shot in the shoulder is the time-tested method of vaccination.

As modern molecular biology greeted the genetic revolution, a new class of vaccines has generated excitement. The DNA vaccine -- in which a piece of naked DNA, rather than an antigenic protein, is injected -- has been hyped as ensuring effectiveness without the possibility of infection. Unlike sub-unit preparations, DNA vaccines don't require refrigeration. Still, they may be prohibitively expensive to produce.

Pick a plant, like the tomato or potato, that can be easily engineered to express foreign proteins.

Engineer it to contain carefully selected DNA fragments (which let the plant produce the antigens) from the target germ.

Give the plant a signal so it will make the protein in its tissues.

Grind up or dehydrate the antigen-bearing tissue, and there you have it: vaccine magic.

Tricky beginnings
In the early 1990's, researchers imagined that edible vaccines would be as safe as sub-unit preparations, while bypassing much of the cost and the need for refrigeration.

Still, there were plenty of unknowns:

Which plants would best carry and express antigen genes?

Would ingested vaccines be degraded in the hostile, acidic stomach before the immune system could see them?

Would the immune response be enough to defend against infection?

And would the technology pass stringent clinical trials?

A decade later, plant-derived vaccines have blossomed into a full-fledged field of research, with answers to some, but not all, of those questions. The biggest obstacle, at this point, appears to be dosage. Too high a dose could provoke tolerance of an invading germ instead of immunity. Too low a dose could fail to provoke immunity.

Because, on a given plant, some fruits have a bigger percentage of a protein than others, and the fruits vary in size, the dose can't be measured by the banana. Instead, plant-based vaccines will have to be processed -- using widely available technology -- into pills, puddings, or chips.

From USDA Image Gallery, at the Fruits/Veggies link.

Now that dosing difficulties have thrown a spanner into the original vision, conferring immunity to children by simply offering them a fresh-picked banana, Arntzen and others have dropped "edible vaccine" in favor of "plant-derived vaccine."

"We've spent the last three years figuring out how to make uniform doses, large lots, and ensuring that we can do all of the quality assurance things the pharmaceutical industry requires," Arntzen says. "Now the vaccine producers look at our work and say, now this makes sense."

We wouldn't take sides, but edible vaccines really are better for you.

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