Roadkill and smashed grillwork have become common roadside sights as deer expand into urban areas and people expand into rural ones.

The skyrocketing deer population in the United States accounts for 1 billion dollars in property damage and more than 100 human deaths every year.

But a new vaccine hopes to subtract from deer multiplication. The injection destroys gonadotropin [Go-nad-uh-trō-pən]-releasing hormone, which serves as a type of master switch, turning on production of the sex hormones that put deer in the mood. Treated animals lose their sex drive for up to five years, reducing deer numbers and their need to chase or be chased as days grow short.

The drawback is that animals must be caught and sedated for treatment, which takes both time and financial resources. But protecting cars, deer and especially human bodies may be well worth it.