Human papillomavirus (hpv) is an unwelcome consequence of a joyful pursuit. Skin-to-skin contact during sex allows the virus to spread, which can lead to genital warts and cancers of the reproductive system. In Britain hpv causes about 3,500 cases of cervical cancer each year and 900 deaths. A vaccination programme that inoculates against the virus"once a runaway success"is floundering.