The HPV vaccine works, and the cervical cancer data now prove it in real populations

The question of whether the HPV vaccine prevents cervical cancer — not just the precancerous lesions the licensing trials measured — has now been answered in whole national populations, and the answer is yes. In England, cervical cancer rates among women offered the vaccine at ages 12-13 were 87% lower than in unvaccinated cohorts [s2]. In Sweden, vaccinated women had roughly a two-thirds lower risk of invasive cervical cancer, and the reduction was largest among those vaccinated youngest [s1].

These are the studies the field waited more than a decade for. Because cervical cancer takes years to develop, the original trials could only show the vaccine prevented the infections and lesions that precede it. Confirming that fewer women actually get the cancer required following national cohorts long enough for cases to appear or not appear.

Sweden: 1.7 million women followed to age 30

The first population-level cancer evidence came from a nationwide Swedish study that followed 1,672,983 girls and women aged 10 to 30 from 2006 through 2017, linking vaccination records to cancer diagnoses [s1]. Over the period, invasive cervical cancer was diagnosed in 19 women who had received the quadrivalent vaccine and 538 who had not [s1].

Translated to rates, the cumulative incidence was 47 cases per 100,000 among vaccinated women and 94 per 100,000 among the unvaccinated [s1]. After adjusting for age and other factors, the incidence rate ratio was 0.37 — a 63% lower risk [s1]. Timing mattered: the rate ratio was 0.12 among women vaccinated before age 17, against 0.47 among those vaccinated at 17 to 30 [s1]. Vaccinating earlier, before likely exposure to the virus, produced the larger benefit.

England: an 87% reduction, and CIN3 nearly eliminated

The English study used cancer-registry data to compare three vaccinated cohorts against earlier cohorts too old to have been offered the bivalent vaccine, which the country introduced in September 2008 [s2]. Drawing on 13.7 million person-years of follow-up in women aged 20 to under 30, it estimated the reduction in cervical cancer by the age at which the vaccine had been offered [s2].

The reductions tracked age at offer closely: 34% for those offered the vaccine at 16-18, 62% at 14-16, and 87% at 12-13, all compared with the unvaccinated reference cohort [s2]. The effect on grade 3 cervical intraepithelial neoplasia (CIN3), the immediate precursor lesion, was even larger — reductions of 39%, 75% and 97% across the same age bands [s2]. The researchers estimated that by mid-2019 the programme had prevented roughly 448 cervical cancers and 17,235 cases of CIN3 [s2], and concluded it "has successfully almost eliminated cervical cancer in women born since Sept 1, 1995" [s2].

Why the age pattern is the crucial detail

Both studies land on the same practical point: the vaccine's benefit is greatest when it is given before exposure to HPV, which is why national programmes target early adolescence rather than adulthood [s1] [s2]. The vaccine is a preventive, not a treatment — it stops new infections with the virus types it covers, so its power falls once someone has already been exposed. The steep gradient from the 12-13 group to the older groups in both countries is the fingerprint of that biology, not a flaw in the vaccine.

The limits, stated plainly

These are observational studies, not randomised trials, so they cannot fully exclude that vaccinated and unvaccinated women differ in other ways — though both adjusted for known confounders, and the English design accounted for changes in screening policy over the period [s1] [s2]. They measure the older bivalent and quadrivalent vaccines, not the current nine-valent product, and they follow women only into their 20s, so the full lifetime effect is still accruing. Vaccination also does not remove the need for cervical screening, because the vaccines do not cover every cancer-causing HPV type [s1] [s2].

What the data do establish is no longer in serious doubt: at a population scale, HPV vaccination sharply reduces invasive cervical cancer, most of all when given young [s1] [s2]. That is a stronger, more concrete claim than the trials could make, and it is now supported by the cancer counts themselves.

Sources

• HPV Vaccination and the Risk of Invasive Cervical Cancer — New England Journal of Medicine, 2020-10-01
• The effects of the national HPV vaccination programme in England, UK, on cervical cancer and grade 3 cervical intraepithelial neoplasia incidence — The Lancet, 2021-11-03