The vaccine isn't ready for use. So far, it's in the earliest stages of testing on rats, with no human studies on the horizon yet.
Such a vaccine would target ghrelin, a hunger hormone that stimulates the appetite.
While the vaccine is far from its final form, it's an obesityobesity-fighting possibility that deserves further research, according to the scientists who are working on the vaccine.
They include Eric Zorrilla, PhD, of the Skaggs Institute for Chemical Biology in La Jolla, Calif. Their study appears in Proceedings of the National Academy of Sciences' early online edition.
Mice without ghrelin genes burn more calories, move more, and store less fat on high-calorie diets, note Zorrilla and colleagues.
They developed three experimental vaccines, each targeting a different part of ghrelin's chemical structure, and tested the vaccines on adult male rats.
The rats didn't have extra weight to lose. They were lean. They were also on a low-calorie, low-fat diet that wasn't too tasty, note Zorrilla and colleagues.
The researchers vaccinated one group of rats five times over 12 weeks. For comparison, they didn't vaccinate other rats.
During the study, the vaccinated mice ate just as much as the unvaccinated mice but gained less weight, the study shows.
Vaccination against ghrelin "appears to be a viable method to slow weight gain and fat accrual in mammals," the researchers write.
If ghrelin is a hunger hormone, why didn't the vaccinated rats lose their appetite? The low-fat rat chow may have had something to do with that.
Other studies have shown that mice without ghrelin receptors eat less on high-fat diets; low-fat diets may not yield the same effect, Zorrilla's team explains.
Many questions remain about a possible ghrelin vaccine, and it's too soon to know the answers.
The researchers don't know if the vaccine would work the same way in overweight or obese rats, or with a typical Western diet that's high in fat and calories.
Also, the test only lasted for about three months. Long-term effects and safety aren't yet known.
And of course, the vaccine isn't ready for testing on people.