HPV

HPV stands for human papillomavirus. The World Health Organization describes it as a common sexually transmitted infection which can affect the skin, genital area, anal area and throat, and is blunt about how common: almost all sexually active people will be infected at some point, usually without symptoms, and in most cases the immune system clears the virus naturally.

That last point is why the word infection can mislead here. For the great majority of people an HPV infection is a passing event they never learn about. The risk comes from a minority of infections that persist, and from a subset of types classed as high risk or oncogenic. WHO states that almost all cases of cervical cancer are caused by infection with oncogenic types of HPV, with types 16 and 18 alone responsible for around 76 percent of them.

This combination, an extremely common virus and a rare but serious outcome from a few of its types, is what makes vaccination effective at a population level. A vaccine given before exposure prevents infection by the types it covers, and because those types cause most cervical cancer, preventing them removes most of the eventual disease. The delay between the two is long, which is why results take decades to read.