"Sexual activity" as used in this section means sexual contact between human beings, consisting of contact between the penis and the vulva, the penis and the anus, the mouth and the penis, the mouth and the vulva, or the mouth and the anus, and includes any sexual contact as defined in §
8.6-53. For the purposes of this chapter, sexual contact between the penis and the vulva, or between the penis and the anus, occurs upon penetration, however slight. Emission is not required.