HPV, and what the vaccine actually prevents

Human papillomavirus is the most common sexually transmitted infection in the world, and the majority of sexually active people acquire at least one type at some point.

What it is

A family of well over a hundred related viruses, of which around forty affect the genital area.

Most are transient: the immune system clears the infection within one to two years, with no symptoms and no consequences, and the person never knows.

A minority are high-risk types capable of causing persistent infection, and it is persistence rather than infection that leads to cellular changes over years or decades.

A separate group of low-risk types causes genital warts, which are unpleasant and are not associated with cancer.

The cancers involved

Virtually all cervical cancer is caused by high-risk HPV, which is one of the strongest causal relationships known in oncology.

HPV also causes a substantial proportion of anal, vaginal, vulval and penile cancers, and a rising proportion of oropharyngeal cancers — cancers of the tonsil and base of tongue — which now affect men more commonly than women in several countries.

Which is why vaccination programmes that initially targeted girls have been extended to boys in many countries: the burden is not confined to cervical disease.

The vaccine

It protects against the types responsible for the great majority of HPV-related cancers, and the newer formulations cover more types including those causing warts.

It is prophylactic rather than therapeutic — it prevents acquisition and does not treat existing infection — which is why it is given before sexual activity begins, typically in early adolescence, and why two doses given young produce the same protection as three given later.

Real-world data from countries with high uptake has been striking: substantial falls in vaccine-type infections, in high-grade cervical abnormalities, and in genital warts, with population studies now showing reductions in cervical cancer incidence in vaccinated cohorts.

Herd effects have reduced infection in unvaccinated people as well.

Safety monitoring across enormous numbers of doses has not identified serious safety signals, and the concerns that circulated in some countries were investigated extensively and not substantiated.

Vaccination after the routine age is still available in many places and offers some benefit to those not already exposed to the covered types, though the benefit is smaller.

Screening still matters

The point most often misunderstood.

The vaccine does not cover every oncogenic type, and vaccinated people still require cervical screening according to their national programme.

Screening itself has changed substantially: most programmes have moved to testing for high-risk HPV first, with cytology performed only on positive samples, because HPV testing is more sensitive and a negative test provides longer reassurance.

Which is why intervals have lengthened in several countries — not a reduction in care but a consequence of a better test.

Self-sampling for HPV is being introduced in a number of programmes and substantially increases participation among people who do not attend for a speculum examination.

What a positive result means

Not that anything is wrong now, and not that a partner has been unfaithful.

HPV can remain dormant for years, so detection says nothing reliable about when it was acquired or from whom, and this is worth knowing before it causes an unnecessary crisis in a relationship.

A positive HPV test with normal cells generally means repeat testing at an interval, since most infections clear.

Abnormal cells are graded, and low-grade changes frequently resolve without treatment.

High-grade changes are treated with a procedure removing the affected area, which is highly effective and carries a small increased risk in future pregnancies that is discussed at the time.

Warts

Common, benign and disproportionately distressing.

Treatments include topical agents applied at home and physical removal in clinic, and none of them eradicate the virus itself, which the immune system does over time.

Recurrence in the months after treatment is common and does not indicate reinfection.

Condoms reduce transmission and do not eliminate it, since the virus is present on skin not covered.

What to take from it

HPV is close to a universal human experience rather than a marker of anything about a person's behaviour.

Vaccination is among the small number of interventions that prevent cancer outright rather than detecting it early.

And screening remains the thing that catches the small fraction of infections that would otherwise progress, which is why attendance rates matter more than almost any other measure in this area.

General information only, not medical advice. Vaccination and screening programmes vary by country — consult a qualified clinician or your national screening service.