Using helicopters, airplanes, and automobiles, the U.S. Department of Agriculture (USDA) has begun distributing an oral rabies vaccine designed to inoculate raccoons in 10 eastern states. The annual vaccination campaign is part of a long-running effort by the USDA to control the spread of the deadly viral disease to humans by immunizing the wild animals that most often transmit it.

Rabies kills about 60,000 people annually worldwide, according to the World Health Organization. Most of those deaths are caused by rabid dogs. Because the U.S. has strict pet vaccination laws intended to prevent the disease, rabies infections in this country are spread predominantly by wildlife, including raccoons, skunks, foxes, and bats.

The USDA began this year’s vaccine distribution in early August. The agency uses a bait coated with a fishmeal attractant to target raccoons, which are most likely to spread rabies in states along the east coast. Officials hope to keep the raccoon-based strain of rabies from spreading west, according to a press release. Distribution started in the Northeast and Mid-Atlantic and will move south through October. In total, the USDA plans to spread 3.75 million bait packs in parts of Maine, Pennsylvania, West Virginia, Massachusetts, Virginia, North Carolina, South Carolina, Tennessee, Georgia, and Alabama.

The department’s rabies control program has been around since 1997 when it was started by vaccinating coyotes in Texas. The USDA vaccine drops eliminated the variant those coyotes were spreading within seven years, according to the Associated Press.

Each year about 60,000 people in the U.S. encounter a possible exposure to the virus and receive the highly effective post-exposure prophylaxis (PEP) shots that can prevent rabies from developing if administered before symptoms appear. As a result, deaths are rare. In 2021, five people in the U.S. died from rabies infection, the highest number in a decade. The deaths of three people within a five-week period last fall caused the CDC to issue a warning to raise awareness about the risk of contracting rabies from bats and the importance of seeking treatment immediately. The three victims died after encountering bats in or around their homes, and none of them received PEP shots.

Which animal is most likely to carry rabies depends on where you live. While raccoons pose the biggest threat on the eastern seaboard, throughout much of the Midwest the most likely culprits are skunks. Foxes pose the highest risk in parts of Alaska and the desert southwest. Elsewhere, bats are the most common rabies carriers. According to the CDC, infected bats account for 70 percent of all rabies deaths in the U.S.