Cases of Lyme disease might be reduced by switching the focus from people and vaccinating the animals that carry it, a new study suggests.

Writing in The Proceedings of the National Academy of Sciences, researchers described an experiment in which they caught white-footed mice in a wooded area of roughly 3,000 acres in Connecticut, vaccinated them against Lyme disease, tagged them and set them free. The lead author was Dr. Jean Tsao of Michigan State University.

The mice are among the food sources for ticks, which pass the disease to humans though bites. Over the four years of mouse vaccinations, the researchers found that the level of infection among ticks also went down.

The findings hold out hope not only for reducing the incidence of Lyme disease but also of other vector-borne illnesses, including West Nile virus, said the study’s principal investigator, Dr. Durland Fish, an epidemiologist at Yale. The disease-causing microbes are passed from animal to animal by ticks, mosquitoes and other insects.

Giving shots to countless numbers of mice is impractical, of course, but the vaccine can also be given in food, as is done to fight rabies. Research on human vaccines has been conducted, but none are now on the market.

The study also made clear, however, that with Lyme disease the picture was more complicated than had been believed. The researchers found that mice caused perhaps 27 percent to 55 percent of the infections, fewer than they had expected, Dr. Fish said.

That means that the vaccinations would also have to be put in food eaten by other animals that play a role. Birds, Dr. Fish said, are prime suspects.