In 2011, a young girl bitten by a rabid stray cat survived without the vaccine, only one of 3 known to do so. She lived in Willow Creek, CA, where most of this story takes place.
Louis Pasteur developed the rabies vaccine in 1885. He developed the anthrax vaccine in the 1870s. The episode previous to this one showed them vaccinating some cattle for anthrax. In this one, it is stated that there is no known cure for rabies. Without knowing just which year the episode takes place, it is possible that the rabies vaccine had not yet been developed.
Julia (Nancy Olson), an unmarried mother, wants Nick (Peter Breck) to marry her to give her son, Tommy (Ron Howard), a good name. She then wants to take Tommy to Massachusetts. Nick fulfills her wish after she is killed. Peter Breck was born in Haverhill, MA.
Nick tells Heath about a girl he once met at Willow Springs, California. Heath says that is near Napa, which Nick confirms. Later, when Nick goes away from the Barkley Ranch, he tells his mother he is going to Vallejo, which is near Napa. However, the only Willow Springs in the state are one in Mono County, east of the Sierra, one in Kern County, hundreds of miles to the south, one in Riverside County, even farther south, and one in Tuolumne County, about 70 miles east of Stockton, in the opposite direction of Vallejo and Napa.